diff --git a/backend/internal/handlers/calculate.go b/backend/internal/handlers/calculate.go
new file mode 100644
index 0000000..7637fdd
--- /dev/null
+++ b/backend/internal/handlers/calculate.go
@@ -0,0 +1,89 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"time"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+)
+
+// CalculateHandlers holds handlers for deadline calculation endpoints
+type CalculateHandlers struct {
+	calculator *services.DeadlineCalculator
+	rules      *services.DeadlineRuleService
+}
+
+// NewCalculateHandlers creates calculate handlers
+func NewCalculateHandlers(calc *services.DeadlineCalculator, rules *services.DeadlineRuleService) *CalculateHandlers {
+	return &CalculateHandlers{calculator: calc, rules: rules}
+}
+
+// CalculateRequest is the input for POST /api/deadlines/calculate
+type CalculateRequest struct {
+	ProceedingType   string   `json:"proceeding_type"`
+	TriggerEventDate string   `json:"trigger_event_date"`
+	SelectedRuleIDs  []string `json:"selected_rule_ids,omitempty"`
+}
+
+// Calculate handles POST /api/deadlines/calculate
+func (h *CalculateHandlers) Calculate(w http.ResponseWriter, r *http.Request) {
+	var req CalculateRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+
+	if req.ProceedingType == "" || req.TriggerEventDate == "" {
+		writeError(w, http.StatusBadRequest, "proceeding_type and trigger_event_date are required")
+		return
+	}
+
+	eventDate, err := time.Parse("2006-01-02", req.TriggerEventDate)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid trigger_event_date format, expected YYYY-MM-DD")
+		return
+	}
+
+	var results []services.CalculatedDeadline
+
+	if len(req.SelectedRuleIDs) > 0 {
+		ruleModels, err := h.rules.GetByIDs(req.SelectedRuleIDs)
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "failed to fetch selected rules")
+			return
+		}
+		results = h.calculator.CalculateFromRules(eventDate, ruleModels)
+	} else {
+		tree, err := h.rules.GetRuleTree(req.ProceedingType)
+		if err != nil {
+			writeError(w, http.StatusBadRequest, "unknown proceeding type")
+			return
+		}
+		// Flatten tree to get all rule models
+		var flatNodes []services.RuleTreeNode
+		flattenTree(tree, &flatNodes)
+
+		ruleModels := make([]models.DeadlineRule, 0, len(flatNodes))
+		for _, node := range flatNodes {
+			ruleModels = append(ruleModels, node.DeadlineRule)
+		}
+		results = h.calculator.CalculateFromRules(eventDate, ruleModels)
+	}
+
+	writeJSON(w, http.StatusOK, map[string]any{
+		"proceeding_type":    req.ProceedingType,
+		"trigger_event_date": req.TriggerEventDate,
+		"deadlines":          results,
+	})
+}
+
+func flattenTree(nodes []services.RuleTreeNode, result *[]services.RuleTreeNode) {
+	for _, n := range nodes {
+		*result = append(*result, n)
+		if len(n.Children) > 0 {
+			flattenTree(n.Children, result)
+		}
+	}
+}
diff --git a/backend/internal/handlers/deadline_rules.go b/backend/internal/handlers/deadline_rules.go
new file mode 100644
index 0000000..6c410b1
--- /dev/null
+++ b/backend/internal/handlers/deadline_rules.go
@@ -0,0 +1,58 @@
+package handlers
+
+import (
+	"net/http"
+	"strconv"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+)
+
+// DeadlineRuleHandlers holds handlers for deadline rule endpoints
+type DeadlineRuleHandlers struct {
+	rules *services.DeadlineRuleService
+}
+
+// NewDeadlineRuleHandlers creates deadline rule handlers
+func NewDeadlineRuleHandlers(rs *services.DeadlineRuleService) *DeadlineRuleHandlers {
+	return &DeadlineRuleHandlers{rules: rs}
+}
+
+// List handles GET /api/deadline-rules
+// Query params: proceeding_type_id (optional int filter)
+func (h *DeadlineRuleHandlers) List(w http.ResponseWriter, r *http.Request) {
+	var proceedingTypeID *int
+	if v := r.URL.Query().Get("proceeding_type_id"); v != "" {
+		id, err := strconv.Atoi(v)
+		if err != nil {
+			writeError(w, http.StatusBadRequest, "invalid proceeding_type_id")
+			return
+		}
+		proceedingTypeID = &id
+	}
+
+	rules, err := h.rules.List(proceedingTypeID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to list deadline rules")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, rules)
+}
+
+// GetRuleTree handles GET /api/deadline-rules/{type}
+// {type} is the proceeding type code (e.g., "INF", "REV")
+func (h *DeadlineRuleHandlers) GetRuleTree(w http.ResponseWriter, r *http.Request) {
+	typeCode := r.PathValue("type")
+	if typeCode == "" {
+		writeError(w, http.StatusBadRequest, "proceeding type code required")
+		return
+	}
+
+	tree, err := h.rules.GetRuleTree(typeCode)
+	if err != nil {
+		writeError(w, http.StatusNotFound, "proceeding type not found")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, tree)
+}
diff --git a/backend/internal/handlers/deadlines.go b/backend/internal/handlers/deadlines.go
new file mode 100644
index 0000000..844d243
--- /dev/null
+++ b/backend/internal/handlers/deadlines.go
@@ -0,0 +1,162 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/jmoiron/sqlx"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+)
+
+// DeadlineHandlers holds handlers for deadline CRUD endpoints
+type DeadlineHandlers struct {
+	deadlines *services.DeadlineService
+	db        *sqlx.DB
+}
+
+// NewDeadlineHandlers creates deadline handlers
+func NewDeadlineHandlers(ds *services.DeadlineService, db *sqlx.DB) *DeadlineHandlers {
+	return &DeadlineHandlers{deadlines: ds, db: db}
+}
+
+// ListForCase handles GET /api/cases/{caseID}/deadlines
+func (h *DeadlineHandlers) ListForCase(w http.ResponseWriter, r *http.Request) {
+	tenantID, err := resolveTenant(r, h.db)
+	if err != nil {
+		handleTenantError(w, err)
+		return
+	}
+
+	caseID, err := parsePathUUID(r, "caseID")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid case ID")
+		return
+	}
+
+	deadlines, err := h.deadlines.ListForCase(tenantID, caseID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to list deadlines")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, deadlines)
+}
+
+// Create handles POST /api/cases/{caseID}/deadlines
+func (h *DeadlineHandlers) Create(w http.ResponseWriter, r *http.Request) {
+	tenantID, err := resolveTenant(r, h.db)
+	if err != nil {
+		handleTenantError(w, err)
+		return
+	}
+
+	caseID, err := parsePathUUID(r, "caseID")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid case ID")
+		return
+	}
+
+	var input services.CreateDeadlineInput
+	if err := json.NewDecoder(r.Body).Decode(&input); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+	input.CaseID = caseID
+
+	if input.Title == "" || input.DueDate == "" {
+		writeError(w, http.StatusBadRequest, "title and due_date are required")
+		return
+	}
+
+	deadline, err := h.deadlines.Create(tenantID, input)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to create deadline")
+		return
+	}
+
+	writeJSON(w, http.StatusCreated, deadline)
+}
+
+// Update handles PUT /api/deadlines/{deadlineID}
+func (h *DeadlineHandlers) Update(w http.ResponseWriter, r *http.Request) {
+	tenantID, err := resolveTenant(r, h.db)
+	if err != nil {
+		handleTenantError(w, err)
+		return
+	}
+
+	deadlineID, err := parsePathUUID(r, "deadlineID")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid deadline ID")
+		return
+	}
+
+	var input services.UpdateDeadlineInput
+	if err := json.NewDecoder(r.Body).Decode(&input); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+
+	deadline, err := h.deadlines.Update(tenantID, deadlineID, input)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to update deadline")
+		return
+	}
+	if deadline == nil {
+		writeError(w, http.StatusNotFound, "deadline not found")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, deadline)
+}
+
+// Complete handles PATCH /api/deadlines/{deadlineID}/complete
+func (h *DeadlineHandlers) Complete(w http.ResponseWriter, r *http.Request) {
+	tenantID, err := resolveTenant(r, h.db)
+	if err != nil {
+		handleTenantError(w, err)
+		return
+	}
+
+	deadlineID, err := parsePathUUID(r, "deadlineID")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid deadline ID")
+		return
+	}
+
+	deadline, err := h.deadlines.Complete(tenantID, deadlineID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to complete deadline")
+		return
+	}
+	if deadline == nil {
+		writeError(w, http.StatusNotFound, "deadline not found")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, deadline)
+}
+
+// Delete handles DELETE /api/deadlines/{deadlineID}
+func (h *DeadlineHandlers) Delete(w http.ResponseWriter, r *http.Request) {
+	tenantID, err := resolveTenant(r, h.db)
+	if err != nil {
+		handleTenantError(w, err)
+		return
+	}
+
+	deadlineID, err := parsePathUUID(r, "deadlineID")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid deadline ID")
+		return
+	}
+
+	err = h.deadlines.Delete(tenantID, deadlineID)
+	if err != nil {
+		writeError(w, http.StatusNotFound, err.Error())
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"status": "deleted"})
+}
diff --git a/backend/internal/handlers/helpers.go b/backend/internal/handlers/helpers.go
index ce23c1d..59a7e5a 100644
--- a/backend/internal/handlers/helpers.go
+++ b/backend/internal/handlers/helpers.go
@@ -3,14 +3,83 @@ package handlers
 import (
 	"encoding/json"
 	"net/http"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
 )
 
-func writeJSON(w http.ResponseWriter, status int, v interface{}) {
+func writeJSON(w http.ResponseWriter, status int, v any) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
 	json.NewEncoder(w).Encode(v)
 }
 
-func writeError(w http.ResponseWriter, status int, message string) {
-	writeJSON(w, status, map[string]string{"error": message})
+func writeError(w http.ResponseWriter, status int, msg string) {
+	writeJSON(w, status, map[string]string{"error": msg})
+}
+
+// resolveTenant gets the tenant ID for the authenticated user.
+// Checks X-Tenant-ID header first, then falls back to user's first tenant.
+func resolveTenant(r *http.Request, db *sqlx.DB) (uuid.UUID, error) {
+	userID, ok := auth.UserFromContext(r.Context())
+	if !ok {
+		return uuid.Nil, errUnauthorized
+	}
+
+	// Check header first
+	if headerVal := r.Header.Get("X-Tenant-ID"); headerVal != "" {
+		tenantID, err := uuid.Parse(headerVal)
+		if err != nil {
+			return uuid.Nil, errInvalidTenant
+		}
+		// Verify user has access to this tenant
+		var count int
+		err = db.Get(&count,
+			`SELECT COUNT(*) FROM user_tenants WHERE user_id = $1 AND tenant_id = $2`,
+			userID, tenantID)
+		if err != nil || count == 0 {
+			return uuid.Nil, errTenantAccess
+		}
+		return tenantID, nil
+	}
+
+	// Fall back to user's first tenant
+	var tenantID uuid.UUID
+	err := db.Get(&tenantID,
+		`SELECT tenant_id FROM user_tenants WHERE user_id = $1 ORDER BY created_at LIMIT 1`,
+		userID)
+	if err != nil {
+		return uuid.Nil, errNoTenant
+	}
+	return tenantID, nil
+}
+
+type apiError struct {
+	msg    string
+	status int
+}
+
+func (e *apiError) Error() string { return e.msg }
+
+var (
+	errUnauthorized = &apiError{msg: "unauthorized", status: http.StatusUnauthorized}
+	errInvalidTenant = &apiError{msg: "invalid tenant ID", status: http.StatusBadRequest}
+	errTenantAccess  = &apiError{msg: "no access to tenant", status: http.StatusForbidden}
+	errNoTenant      = &apiError{msg: "no tenant found for user", status: http.StatusBadRequest}
+)
+
+// handleTenantError writes the appropriate error response for tenant resolution errors
+func handleTenantError(w http.ResponseWriter, err error) {
+	if ae, ok := err.(*apiError); ok {
+		writeError(w, ae.status, ae.msg)
+		return
+	}
+	writeError(w, http.StatusInternalServerError, "internal error")
+}
+
+// parsePathUUID extracts a UUID from the URL path using PathValue
+func parsePathUUID(r *http.Request, key string) (uuid.UUID, error) {
+	return uuid.Parse(r.PathValue(key))
 }
diff --git a/backend/internal/router/router.go b/backend/internal/router/router.go
index 142aab3..4b21e0d 100644
--- a/backend/internal/router/router.go
+++ b/backend/internal/router/router.go
@@ -19,6 +19,10 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	caseSvc := services.NewCaseService(db)
 	partySvc := services.NewPartyService(db)
 	appointmentSvc := services.NewAppointmentService(db)
+	holidaySvc := services.NewHolidayService(db)
+	deadlineSvc := services.NewDeadlineService(db)
+	deadlineRuleSvc := services.NewDeadlineRuleService(db)
+	calculator := services.NewDeadlineCalculator(holidaySvc)
 
 	// Middleware
 	tenantResolver := auth.NewTenantResolver(tenantSvc)
@@ -28,6 +32,9 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	caseH := handlers.NewCaseHandler(caseSvc)
 	partyH := handlers.NewPartyHandler(partySvc)
 	apptH := handlers.NewAppointmentHandler(appointmentSvc)
+	deadlineH := handlers.NewDeadlineHandlers(deadlineSvc, db)
+	ruleH := handlers.NewDeadlineRuleHandlers(deadlineRuleSvc)
+	calcH := handlers.NewCalculateHandlers(calculator, deadlineRuleSvc)
 
 	// Public routes
 	mux.HandleFunc("GET /health", handleHealth(db))
@@ -59,6 +66,20 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	scoped.HandleFunc("PUT /api/parties/{partyId}", partyH.Update)
 	scoped.HandleFunc("DELETE /api/parties/{partyId}", partyH.Delete)
 
+	// Deadlines
+	scoped.HandleFunc("GET /api/cases/{caseID}/deadlines", deadlineH.ListForCase)
+	scoped.HandleFunc("POST /api/cases/{caseID}/deadlines", deadlineH.Create)
+	scoped.HandleFunc("PUT /api/deadlines/{deadlineID}", deadlineH.Update)
+	scoped.HandleFunc("PATCH /api/deadlines/{deadlineID}/complete", deadlineH.Complete)
+	scoped.HandleFunc("DELETE /api/deadlines/{deadlineID}", deadlineH.Delete)
+
+	// Deadline rules (reference data)
+	scoped.HandleFunc("GET /api/deadline-rules", ruleH.List)
+	scoped.HandleFunc("GET /api/deadline-rules/{type}", ruleH.GetRuleTree)
+
+	// Deadline calculator
+	scoped.HandleFunc("POST /api/deadlines/calculate", calcH.Calculate)
+
 	// Appointments
 	scoped.HandleFunc("GET /api/appointments", apptH.List)
 	scoped.HandleFunc("POST /api/appointments", apptH.Create)
@@ -66,7 +87,6 @@ func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	scoped.HandleFunc("DELETE /api/appointments/{id}", apptH.Delete)
 
 	// Placeholder routes for future phases
-	scoped.HandleFunc("GET /api/deadlines", placeholder("deadlines"))
 	scoped.HandleFunc("GET /api/documents", placeholder("documents"))
 
 	// Wire: auth -> tenant routes go directly, scoped routes get tenant resolver
diff --git a/backend/internal/services/deadline_calculator.go b/backend/internal/services/deadline_calculator.go
new file mode 100644
index 0000000..80c472e
--- /dev/null
+++ b/backend/internal/services/deadline_calculator.go
@@ -0,0 +1,99 @@
+package services
+
+import (
+	"time"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+)
+
+// CalculatedDeadline holds a calculated deadline with adjustment info
+type CalculatedDeadline struct {
+	RuleCode        string `json:"rule_code"`
+	RuleID          string `json:"rule_id"`
+	Title           string `json:"title"`
+	DueDate         string `json:"due_date"`
+	OriginalDueDate string `json:"original_due_date"`
+	WasAdjusted     bool   `json:"was_adjusted"`
+}
+
+// DeadlineCalculator calculates deadlines from rules and event dates
+type DeadlineCalculator struct {
+	holidays *HolidayService
+}
+
+// NewDeadlineCalculator creates a new calculator
+func NewDeadlineCalculator(holidays *HolidayService) *DeadlineCalculator {
+	return &DeadlineCalculator{holidays: holidays}
+}
+
+// CalculateEndDate calculates the end date for a single deadline rule based on an event date.
+// Adapted from youpc.org CalculateDeadlineEndDate.
+func (c *DeadlineCalculator) CalculateEndDate(eventDate time.Time, rule models.DeadlineRule) (adjusted time.Time, original time.Time, wasAdjusted bool) {
+	endDate := eventDate
+
+	timing := "after"
+	if rule.Timing != nil {
+		timing = *rule.Timing
+	}
+
+	durationValue := rule.DurationValue
+	durationUnit := rule.DurationUnit
+
+	if timing == "before" {
+		switch durationUnit {
+		case "days":
+			endDate = endDate.AddDate(0, 0, -durationValue)
+		case "weeks":
+			endDate = endDate.AddDate(0, 0, -durationValue*7)
+		case "months":
+			endDate = endDate.AddDate(0, -durationValue, 0)
+		}
+	} else {
+		switch durationUnit {
+		case "days":
+			endDate = endDate.AddDate(0, 0, durationValue)
+		case "weeks":
+			endDate = endDate.AddDate(0, 0, durationValue*7)
+		case "months":
+			endDate = endDate.AddDate(0, durationValue, 0)
+		}
+	}
+
+	original = endDate
+	adjusted, _, wasAdjusted = c.holidays.AdjustForNonWorkingDays(endDate)
+	return adjusted, original, wasAdjusted
+}
+
+// CalculateFromRules calculates deadlines for a set of rules given an event date.
+// Returns a list of calculated deadlines with due dates.
+func (c *DeadlineCalculator) CalculateFromRules(eventDate time.Time, rules []models.DeadlineRule) []CalculatedDeadline {
+	results := make([]CalculatedDeadline, 0, len(rules))
+
+	for _, rule := range rules {
+		var adjusted, original time.Time
+		var wasAdjusted bool
+
+		if rule.DurationValue > 0 {
+			adjusted, original, wasAdjusted = c.CalculateEndDate(eventDate, rule)
+		} else {
+			adjusted = eventDate
+			original = eventDate
+		}
+
+		code := ""
+		if rule.Code != nil {
+			code = *rule.Code
+		}
+
+		results = append(results, CalculatedDeadline{
+			RuleCode:        code,
+			RuleID:          rule.ID.String(),
+			Title:           rule.Name,
+			DueDate:         adjusted.Format("2006-01-02"),
+			OriginalDueDate: original.Format("2006-01-02"),
+			WasAdjusted:     wasAdjusted,
+		})
+	}
+
+	return results
+}
diff --git a/backend/internal/services/deadline_calculator_test.go b/backend/internal/services/deadline_calculator_test.go
new file mode 100644
index 0000000..0ab70ab
--- /dev/null
+++ b/backend/internal/services/deadline_calculator_test.go
@@ -0,0 +1,141 @@
+package services
+
+import (
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+)
+
+func TestCalculateEndDateAfterDays(t *testing.T) {
+	holidays := NewHolidayService(nil)
+	calc := NewDeadlineCalculator(holidays)
+
+	eventDate := time.Date(2026, 3, 25, 0, 0, 0, 0, time.UTC) // Wednesday
+	timing := "after"
+	rule := models.DeadlineRule{
+		ID:            uuid.New(),
+		Name:          "Test 10 days",
+		DurationValue: 10,
+		DurationUnit:  "days",
+		Timing:        &timing,
+	}
+
+	adjusted, original, wasAdjusted := calc.CalculateEndDate(eventDate, rule)
+
+	// 25 March + 10 days = 4 April 2026 (Saturday)
+	// Apr 5 = Easter Sunday (holiday), Apr 6 = Easter Monday (holiday) -> adjusted to 7 April (Tuesday)
+	expectedOriginal := time.Date(2026, 4, 4, 0, 0, 0, 0, time.UTC)
+	expectedAdjusted := time.Date(2026, 4, 7, 0, 0, 0, 0, time.UTC)
+
+	if original != expectedOriginal {
+		t.Errorf("original should be %s, got %s", expectedOriginal, original)
+	}
+	if adjusted != expectedAdjusted {
+		t.Errorf("adjusted should be %s, got %s", expectedAdjusted, adjusted)
+	}
+	if !wasAdjusted {
+		t.Error("should have been adjusted (Saturday)")
+	}
+}
+
+func TestCalculateEndDateBeforeMonths(t *testing.T) {
+	holidays := NewHolidayService(nil)
+	calc := NewDeadlineCalculator(holidays)
+
+	eventDate := time.Date(2026, 6, 15, 0, 0, 0, 0, time.UTC) // Monday
+	timing := "before"
+	rule := models.DeadlineRule{
+		ID:            uuid.New(),
+		Name:          "Test 2 months before",
+		DurationValue: 2,
+		DurationUnit:  "months",
+		Timing:        &timing,
+	}
+
+	adjusted, original, wasAdjusted := calc.CalculateEndDate(eventDate, rule)
+
+	// 15 June - 2 months = 15 April 2026 (Wednesday)
+	expected := time.Date(2026, 4, 15, 0, 0, 0, 0, time.UTC)
+
+	if original != expected {
+		t.Errorf("original should be %s, got %s", expected, original)
+	}
+	if adjusted != expected {
+		t.Errorf("adjusted should be %s (not a holiday/weekend), got %s", expected, adjusted)
+	}
+	if wasAdjusted {
+		t.Error("should not have been adjusted (Wednesday)")
+	}
+}
+
+func TestCalculateEndDateWeeks(t *testing.T) {
+	holidays := NewHolidayService(nil)
+	calc := NewDeadlineCalculator(holidays)
+
+	eventDate := time.Date(2026, 3, 25, 0, 0, 0, 0, time.UTC) // Wednesday
+	timing := "after"
+	rule := models.DeadlineRule{
+		ID:            uuid.New(),
+		Name:          "Test 2 weeks",
+		DurationValue: 2,
+		DurationUnit:  "weeks",
+		Timing:        &timing,
+	}
+
+	adjusted, original, _ := calc.CalculateEndDate(eventDate, rule)
+
+	// 25 March + 14 days = 8 April 2026 (Wednesday)
+	expected := time.Date(2026, 4, 8, 0, 0, 0, 0, time.UTC)
+	if original != expected {
+		t.Errorf("original should be %s, got %s", expected, original)
+	}
+	if adjusted != expected {
+		t.Errorf("adjusted should be %s, got %s", expected, adjusted)
+	}
+}
+
+func TestCalculateFromRules(t *testing.T) {
+	holidays := NewHolidayService(nil)
+	calc := NewDeadlineCalculator(holidays)
+
+	eventDate := time.Date(2026, 3, 25, 0, 0, 0, 0, time.UTC)
+	timing := "after"
+	code := "TEST-1"
+
+	rules := []models.DeadlineRule{
+		{
+			ID:            uuid.New(),
+			Code:          &code,
+			Name:          "Rule A",
+			DurationValue: 7,
+			DurationUnit:  "days",
+			Timing:        &timing,
+		},
+		{
+			ID:            uuid.New(),
+			Name:          "Rule B (zero duration)",
+			DurationValue: 0,
+			DurationUnit:  "days",
+		},
+	}
+
+	results := calc.CalculateFromRules(eventDate, rules)
+	if len(results) != 2 {
+		t.Fatalf("expected 2 results, got %d", len(results))
+	}
+
+	// Rule A: 25 March + 7 = 1 April (Wednesday)
+	if results[0].DueDate != "2026-04-01" {
+		t.Errorf("Rule A due date should be 2026-04-01, got %s", results[0].DueDate)
+	}
+	if results[0].RuleCode != "TEST-1" {
+		t.Errorf("Rule A code should be TEST-1, got %s", results[0].RuleCode)
+	}
+
+	// Rule B: zero duration -> event date
+	if results[1].DueDate != "2026-03-25" {
+		t.Errorf("Rule B due date should be 2026-03-25, got %s", results[1].DueDate)
+	}
+}
diff --git a/backend/internal/services/deadline_rule_service.go b/backend/internal/services/deadline_rule_service.go
new file mode 100644
index 0000000..ae6ee1d
--- /dev/null
+++ b/backend/internal/services/deadline_rule_service.go
@@ -0,0 +1,175 @@
+package services
+
+import (
+	"fmt"
+
+	"github.com/jmoiron/sqlx"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+)
+
+// DeadlineRuleService handles deadline rule queries
+type DeadlineRuleService struct {
+	db *sqlx.DB
+}
+
+// NewDeadlineRuleService creates a new deadline rule service
+func NewDeadlineRuleService(db *sqlx.DB) *DeadlineRuleService {
+	return &DeadlineRuleService{db: db}
+}
+
+// List returns deadline rules, optionally filtered by proceeding type
+func (s *DeadlineRuleService) List(proceedingTypeID *int) ([]models.DeadlineRule, error) {
+	var rules []models.DeadlineRule
+	var err error
+
+	if proceedingTypeID != nil {
+		err = s.db.Select(&rules,
+			`SELECT id, proceeding_type_id, parent_id, code, name, description,
+			        primary_party, event_type, is_mandatory, duration_value, duration_unit,
+			        timing, rule_code, deadline_notes, sequence_order, condition_rule_id,
+			        alt_duration_value, alt_duration_unit, alt_rule_code, is_active,
+			        created_at, updated_at
+			 FROM deadline_rules
+			 WHERE proceeding_type_id = $1 AND is_active = true
+			 ORDER BY sequence_order`, *proceedingTypeID)
+	} else {
+		err = s.db.Select(&rules,
+			`SELECT id, proceeding_type_id, parent_id, code, name, description,
+			        primary_party, event_type, is_mandatory, duration_value, duration_unit,
+			        timing, rule_code, deadline_notes, sequence_order, condition_rule_id,
+			        alt_duration_value, alt_duration_unit, alt_rule_code, is_active,
+			        created_at, updated_at
+			 FROM deadline_rules
+			 WHERE is_active = true
+			 ORDER BY proceeding_type_id, sequence_order`)
+	}
+
+	if err != nil {
+		return nil, fmt.Errorf("listing deadline rules: %w", err)
+	}
+	return rules, nil
+}
+
+// RuleTreeNode represents a deadline rule with its children
+type RuleTreeNode struct {
+	models.DeadlineRule
+	Children []RuleTreeNode `json:"children,omitempty"`
+}
+
+// GetRuleTree returns a hierarchical tree of rules for a proceeding type
+func (s *DeadlineRuleService) GetRuleTree(proceedingTypeCode string) ([]RuleTreeNode, error) {
+	// First resolve proceeding type code to ID
+	var pt models.ProceedingType
+	err := s.db.Get(&pt,
+		`SELECT id, code, name, description, jurisdiction, default_color, sort_order, is_active
+		 FROM proceeding_types
+		 WHERE code = $1 AND is_active = true`, proceedingTypeCode)
+	if err != nil {
+		return nil, fmt.Errorf("resolving proceeding type %q: %w", proceedingTypeCode, err)
+	}
+
+	// Get all rules for this proceeding type
+	var rules []models.DeadlineRule
+	err = s.db.Select(&rules,
+		`SELECT id, proceeding_type_id, parent_id, code, name, description,
+		        primary_party, event_type, is_mandatory, duration_value, duration_unit,
+		        timing, rule_code, deadline_notes, sequence_order, condition_rule_id,
+		        alt_duration_value, alt_duration_unit, alt_rule_code, is_active,
+		        created_at, updated_at
+		 FROM deadline_rules
+		 WHERE proceeding_type_id = $1 AND is_active = true
+		 ORDER BY sequence_order`, pt.ID)
+	if err != nil {
+		return nil, fmt.Errorf("listing rules for type %q: %w", proceedingTypeCode, err)
+	}
+
+	return buildTree(rules), nil
+}
+
+// GetByIDs returns deadline rules by their IDs
+func (s *DeadlineRuleService) GetByIDs(ids []string) ([]models.DeadlineRule, error) {
+	if len(ids) == 0 {
+		return nil, nil
+	}
+
+	query, args, err := sqlx.In(
+		`SELECT id, proceeding_type_id, parent_id, code, name, description,
+		        primary_party, event_type, is_mandatory, duration_value, duration_unit,
+		        timing, rule_code, deadline_notes, sequence_order, condition_rule_id,
+		        alt_duration_value, alt_duration_unit, alt_rule_code, is_active,
+		        created_at, updated_at
+		 FROM deadline_rules
+		 WHERE id IN (?) AND is_active = true
+		 ORDER BY sequence_order`, ids)
+	if err != nil {
+		return nil, fmt.Errorf("building IN query: %w", err)
+	}
+	query = s.db.Rebind(query)
+
+	var rules []models.DeadlineRule
+	err = s.db.Select(&rules, query, args...)
+	if err != nil {
+		return nil, fmt.Errorf("fetching rules by IDs: %w", err)
+	}
+	return rules, nil
+}
+
+// GetRulesForProceedingType returns all active rules for a proceeding type ID
+func (s *DeadlineRuleService) GetRulesForProceedingType(proceedingTypeID int) ([]models.DeadlineRule, error) {
+	var rules []models.DeadlineRule
+	err := s.db.Select(&rules,
+		`SELECT id, proceeding_type_id, parent_id, code, name, description,
+		        primary_party, event_type, is_mandatory, duration_value, duration_unit,
+		        timing, rule_code, deadline_notes, sequence_order, condition_rule_id,
+		        alt_duration_value, alt_duration_unit, alt_rule_code, is_active,
+		        created_at, updated_at
+		 FROM deadline_rules
+		 WHERE proceeding_type_id = $1 AND is_active = true
+		 ORDER BY sequence_order`, proceedingTypeID)
+	if err != nil {
+		return nil, fmt.Errorf("listing rules for proceeding type %d: %w", proceedingTypeID, err)
+	}
+	return rules, nil
+}
+
+// ListProceedingTypes returns all active proceeding types
+func (s *DeadlineRuleService) ListProceedingTypes() ([]models.ProceedingType, error) {
+	var types []models.ProceedingType
+	err := s.db.Select(&types,
+		`SELECT id, code, name, description, jurisdiction, default_color, sort_order, is_active
+		 FROM proceeding_types
+		 WHERE is_active = true
+		 ORDER BY sort_order`)
+	if err != nil {
+		return nil, fmt.Errorf("listing proceeding types: %w", err)
+	}
+	return types, nil
+}
+
+// buildTree converts a flat list of rules into a hierarchical tree
+func buildTree(rules []models.DeadlineRule) []RuleTreeNode {
+	nodeMap := make(map[string]*RuleTreeNode, len(rules))
+	var roots []RuleTreeNode
+
+	// Create nodes
+	for _, r := range rules {
+		node := RuleTreeNode{DeadlineRule: r}
+		nodeMap[r.ID.String()] = &node
+	}
+
+	// Build tree
+	for _, r := range rules {
+		node := nodeMap[r.ID.String()]
+		if r.ParentID != nil {
+			parentKey := r.ParentID.String()
+			if parent, ok := nodeMap[parentKey]; ok {
+				parent.Children = append(parent.Children, *node)
+				continue
+			}
+		}
+		roots = append(roots, *node)
+	}
+
+	return roots
+}
diff --git a/backend/internal/services/deadline_service.go b/backend/internal/services/deadline_service.go
new file mode 100644
index 0000000..4923e13
--- /dev/null
+++ b/backend/internal/services/deadline_service.go
@@ -0,0 +1,180 @@
+package services
+
+import (
+	"database/sql"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+)
+
+// DeadlineService handles CRUD operations for case deadlines
+type DeadlineService struct {
+	db *sqlx.DB
+}
+
+// NewDeadlineService creates a new deadline service
+func NewDeadlineService(db *sqlx.DB) *DeadlineService {
+	return &DeadlineService{db: db}
+}
+
+// ListForCase returns all deadlines for a case, scoped to tenant
+func (s *DeadlineService) ListForCase(tenantID, caseID uuid.UUID) ([]models.Deadline, error) {
+	query := `SELECT id, tenant_id, case_id, title, description, due_date, original_due_date,
+	                 warning_date, source, rule_id, status, completed_at,
+	                 caldav_uid, caldav_etag, notes, created_at, updated_at
+	          FROM deadlines
+	          WHERE tenant_id = $1 AND case_id = $2
+	          ORDER BY due_date ASC`
+
+	var deadlines []models.Deadline
+	err := s.db.Select(&deadlines, query, tenantID, caseID)
+	if err != nil {
+		return nil, fmt.Errorf("listing deadlines for case: %w", err)
+	}
+	return deadlines, nil
+}
+
+// GetByID returns a single deadline by ID, scoped to tenant
+func (s *DeadlineService) GetByID(tenantID, deadlineID uuid.UUID) (*models.Deadline, error) {
+	query := `SELECT id, tenant_id, case_id, title, description, due_date, original_due_date,
+	                 warning_date, source, rule_id, status, completed_at,
+	                 caldav_uid, caldav_etag, notes, created_at, updated_at
+	          FROM deadlines
+	          WHERE tenant_id = $1 AND id = $2`
+
+	var d models.Deadline
+	err := s.db.Get(&d, query, tenantID, deadlineID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("getting deadline: %w", err)
+	}
+	return &d, nil
+}
+
+// CreateDeadlineInput holds the fields for creating a deadline
+type CreateDeadlineInput struct {
+	CaseID      uuid.UUID  `json:"case_id"`
+	Title       string     `json:"title"`
+	Description *string    `json:"description,omitempty"`
+	DueDate     string     `json:"due_date"`
+	WarningDate *string    `json:"warning_date,omitempty"`
+	Source      string     `json:"source"`
+	RuleID      *uuid.UUID `json:"rule_id,omitempty"`
+	Notes       *string    `json:"notes,omitempty"`
+}
+
+// Create inserts a new deadline
+func (s *DeadlineService) Create(tenantID uuid.UUID, input CreateDeadlineInput) (*models.Deadline, error) {
+	id := uuid.New()
+	source := input.Source
+	if source == "" {
+		source = "manual"
+	}
+
+	query := `INSERT INTO deadlines (id, tenant_id, case_id, title, description, due_date,
+	                                  warning_date, source, rule_id, status, notes,
+	                                  created_at, updated_at)
+	          VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, 'pending', $10, NOW(), NOW())
+	          RETURNING id, tenant_id, case_id, title, description, due_date, original_due_date,
+	                    warning_date, source, rule_id, status, completed_at,
+	                    caldav_uid, caldav_etag, notes, created_at, updated_at`
+
+	var d models.Deadline
+	err := s.db.Get(&d, query, id, tenantID, input.CaseID, input.Title, input.Description,
+		input.DueDate, input.WarningDate, source, input.RuleID, input.Notes)
+	if err != nil {
+		return nil, fmt.Errorf("creating deadline: %w", err)
+	}
+	return &d, nil
+}
+
+// UpdateDeadlineInput holds the fields for updating a deadline
+type UpdateDeadlineInput struct {
+	Title       *string    `json:"title,omitempty"`
+	Description *string    `json:"description,omitempty"`
+	DueDate     *string    `json:"due_date,omitempty"`
+	WarningDate *string    `json:"warning_date,omitempty"`
+	Notes       *string    `json:"notes,omitempty"`
+	Status      *string    `json:"status,omitempty"`
+	RuleID      *uuid.UUID `json:"rule_id,omitempty"`
+}
+
+// Update modifies an existing deadline
+func (s *DeadlineService) Update(tenantID, deadlineID uuid.UUID, input UpdateDeadlineInput) (*models.Deadline, error) {
+	// First check it exists and belongs to tenant
+	existing, err := s.GetByID(tenantID, deadlineID)
+	if err != nil {
+		return nil, err
+	}
+	if existing == nil {
+		return nil, nil
+	}
+
+	query := `UPDATE deadlines SET
+	            title = COALESCE($1, title),
+	            description = COALESCE($2, description),
+	            due_date = COALESCE($3, due_date),
+	            warning_date = COALESCE($4, warning_date),
+	            notes = COALESCE($5, notes),
+	            status = COALESCE($6, status),
+	            rule_id = COALESCE($7, rule_id),
+	            updated_at = NOW()
+	          WHERE id = $8 AND tenant_id = $9
+	          RETURNING id, tenant_id, case_id, title, description, due_date, original_due_date,
+	                    warning_date, source, rule_id, status, completed_at,
+	                    caldav_uid, caldav_etag, notes, created_at, updated_at`
+
+	var d models.Deadline
+	err = s.db.Get(&d, query, input.Title, input.Description, input.DueDate,
+		input.WarningDate, input.Notes, input.Status, input.RuleID,
+		deadlineID, tenantID)
+	if err != nil {
+		return nil, fmt.Errorf("updating deadline: %w", err)
+	}
+	return &d, nil
+}
+
+// Complete marks a deadline as completed
+func (s *DeadlineService) Complete(tenantID, deadlineID uuid.UUID) (*models.Deadline, error) {
+	query := `UPDATE deadlines SET
+	            status = 'completed',
+	            completed_at = $1,
+	            updated_at = NOW()
+	          WHERE id = $2 AND tenant_id = $3
+	          RETURNING id, tenant_id, case_id, title, description, due_date, original_due_date,
+	                    warning_date, source, rule_id, status, completed_at,
+	                    caldav_uid, caldav_etag, notes, created_at, updated_at`
+
+	var d models.Deadline
+	err := s.db.Get(&d, query, time.Now(), deadlineID, tenantID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("completing deadline: %w", err)
+	}
+	return &d, nil
+}
+
+// Delete removes a deadline
+func (s *DeadlineService) Delete(tenantID, deadlineID uuid.UUID) error {
+	query := `DELETE FROM deadlines WHERE id = $1 AND tenant_id = $2`
+	result, err := s.db.Exec(query, deadlineID, tenantID)
+	if err != nil {
+		return fmt.Errorf("deleting deadline: %w", err)
+	}
+	rows, err := result.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("checking delete result: %w", err)
+	}
+	if rows == 0 {
+		return fmt.Errorf("deadline not found")
+	}
+	return nil
+}
diff --git a/backend/internal/services/holidays.go b/backend/internal/services/holidays.go
new file mode 100644
index 0000000..806cc51
--- /dev/null
+++ b/backend/internal/services/holidays.go
@@ -0,0 +1,193 @@
+package services
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/jmoiron/sqlx"
+)
+
+// Holiday represents a non-working day
+type Holiday struct {
+	Date       time.Time
+	Name       string
+	IsVacation bool // Part of court vacation period
+	IsClosure  bool // Single-day closure (public holiday)
+}
+
+// HolidayService manages holiday data and non-working day checks
+type HolidayService struct {
+	db *sqlx.DB
+	// Cached holidays by year
+	cache map[int][]Holiday
+}
+
+// NewHolidayService creates a holiday service
+func NewHolidayService(db *sqlx.DB) *HolidayService {
+	return &HolidayService{
+		db:    db,
+		cache: make(map[int][]Holiday),
+	}
+}
+
+// dbHoliday matches the holidays table schema
+type dbHoliday struct {
+	ID          int       `db:"id"`
+	Date        time.Time `db:"date"`
+	Name        string    `db:"name"`
+	Country     string    `db:"country"`
+	State       *string   `db:"state"`
+	HolidayType string    `db:"holiday_type"`
+}
+
+// LoadHolidaysForYear loads holidays from DB for a given year, merges with
+// German federal holidays, and caches the result.
+func (s *HolidayService) LoadHolidaysForYear(year int) ([]Holiday, error) {
+	if cached, ok := s.cache[year]; ok {
+		return cached, nil
+	}
+
+	holidays := make([]Holiday, 0, 30)
+
+	// Load from DB if available
+	if s.db != nil {
+		var dbHolidays []dbHoliday
+		err := s.db.Select(&dbHolidays,
+			`SELECT id, date, name, country, state, holiday_type
+			 FROM holidays
+			 WHERE EXTRACT(YEAR FROM date) = $1
+			 ORDER BY date`, year)
+		if err == nil {
+			for _, h := range dbHolidays {
+				holidays = append(holidays, Holiday{
+					Date:      h.Date,
+					Name:      h.Name,
+					IsClosure: h.HolidayType == "public_holiday" || h.HolidayType == "closure",
+					IsVacation: h.HolidayType == "vacation",
+				})
+			}
+		}
+		// If DB query fails, fall through to hardcoded holidays
+	}
+
+	// Always add German federal holidays (if not already present from DB)
+	federal := germanFederalHolidays(year)
+	existing := make(map[string]bool, len(holidays))
+	for _, h := range holidays {
+		existing[h.Date.Format("2006-01-02")] = true
+	}
+	for _, h := range federal {
+		key := h.Date.Format("2006-01-02")
+		if !existing[key] {
+			holidays = append(holidays, h)
+		}
+	}
+
+	s.cache[year] = holidays
+	return holidays, nil
+}
+
+// IsHoliday checks if a date is a holiday
+func (s *HolidayService) IsHoliday(date time.Time) *Holiday {
+	year := date.Year()
+	holidays, err := s.LoadHolidaysForYear(year)
+	if err != nil {
+		return nil
+	}
+
+	dateStr := date.Format("2006-01-02")
+	for i := range holidays {
+		if holidays[i].Date.Format("2006-01-02") == dateStr {
+			return &holidays[i]
+		}
+	}
+	return nil
+}
+
+// IsNonWorkingDay returns true if the date is a weekend or holiday
+func (s *HolidayService) IsNonWorkingDay(date time.Time) bool {
+	wd := date.Weekday()
+	if wd == time.Saturday || wd == time.Sunday {
+		return true
+	}
+	return s.IsHoliday(date) != nil
+}
+
+// AdjustForNonWorkingDays moves the date to the next working day
+// if it falls on a weekend or holiday.
+// Returns adjusted date, original date, and whether adjustment was made.
+func (s *HolidayService) AdjustForNonWorkingDays(date time.Time) (adjusted time.Time, original time.Time, wasAdjusted bool) {
+	original = date
+	adjusted = date
+
+	// Safety limit: max 30 days forward
+	for i := 0; i < 30 && s.IsNonWorkingDay(adjusted); i++ {
+		adjusted = adjusted.AddDate(0, 0, 1)
+		wasAdjusted = true
+	}
+
+	return adjusted, original, wasAdjusted
+}
+
+// ClearCache clears the holiday cache (useful after DB updates)
+func (s *HolidayService) ClearCache() {
+	s.cache = make(map[int][]Holiday)
+}
+
+// germanFederalHolidays returns all German federal public holidays for a year.
+// These are holidays observed in all 16 German states.
+func germanFederalHolidays(year int) []Holiday {
+	easterMonth, easterDay := CalculateEasterSunday(year)
+	easter := time.Date(year, time.Month(easterMonth), easterDay, 0, 0, 0, 0, time.UTC)
+
+	holidays := []Holiday{
+		{Date: time.Date(year, time.January, 1, 0, 0, 0, 0, time.UTC), Name: "Neujahr", IsClosure: true},
+		{Date: easter.AddDate(0, 0, -2), Name: "Karfreitag", IsClosure: true},
+		{Date: easter, Name: "Ostersonntag", IsClosure: true},
+		{Date: easter.AddDate(0, 0, 1), Name: "Ostermontag", IsClosure: true},
+		{Date: time.Date(year, time.May, 1, 0, 0, 0, 0, time.UTC), Name: "Tag der Arbeit", IsClosure: true},
+		{Date: easter.AddDate(0, 0, 39), Name: "Christi Himmelfahrt", IsClosure: true},
+		{Date: easter.AddDate(0, 0, 49), Name: "Pfingstsonntag", IsClosure: true},
+		{Date: easter.AddDate(0, 0, 50), Name: "Pfingstmontag", IsClosure: true},
+		{Date: time.Date(year, time.October, 3, 0, 0, 0, 0, time.UTC), Name: "Tag der Deutschen Einheit", IsClosure: true},
+		{Date: time.Date(year, time.December, 25, 0, 0, 0, 0, time.UTC), Name: "1. Weihnachtstag", IsClosure: true},
+		{Date: time.Date(year, time.December, 26, 0, 0, 0, 0, time.UTC), Name: "2. Weihnachtstag", IsClosure: true},
+	}
+
+	return holidays
+}
+
+// CalculateEasterSunday computes Easter Sunday using the Anonymous Gregorian algorithm.
+// Returns month (1-12) and day.
+func CalculateEasterSunday(year int) (int, int) {
+	a := year % 19
+	b := year / 100
+	c := year % 100
+	d := b / 4
+	e := b % 4
+	f := (b + 8) / 25
+	g := (b - f + 1) / 3
+	h := (19*a + b - d - g + 15) % 30
+	i := c / 4
+	k := c % 4
+	l := (32 + 2*e + 2*i - h - k) % 7
+	m := (a + 11*h + 22*l) / 451
+	month := (h + l - 7*m + 114) / 31
+	day := ((h + l - 7*m + 114) % 31) + 1
+	return month, day
+}
+
+// GetHolidaysForYear returns all holidays for a year (for API exposure)
+func (s *HolidayService) GetHolidaysForYear(year int) ([]Holiday, error) {
+	return s.LoadHolidaysForYear(year)
+}
+
+// FormatHolidayList returns a simple string representation of holidays for debugging
+func FormatHolidayList(holidays []Holiday) string {
+	var b strings.Builder
+	for _, h := range holidays {
+		fmt.Fprintf(&b, "%s: %s\n", h.Date.Format("2006-01-02"), h.Name)
+	}
+	return b.String()
+}
diff --git a/backend/internal/services/holidays_test.go b/backend/internal/services/holidays_test.go
new file mode 100644
index 0000000..aa8acd3
--- /dev/null
+++ b/backend/internal/services/holidays_test.go
@@ -0,0 +1,121 @@
+package services
+
+import (
+	"testing"
+	"time"
+)
+
+func TestCalculateEasterSunday(t *testing.T) {
+	tests := []struct {
+		year      int
+		wantMonth int
+		wantDay   int
+	}{
+		{2024, 3, 31},
+		{2025, 4, 20},
+		{2026, 4, 5},
+		{2027, 3, 28},
+	}
+
+	for _, tt := range tests {
+		m, d := CalculateEasterSunday(tt.year)
+		if m != tt.wantMonth || d != tt.wantDay {
+			t.Errorf("CalculateEasterSunday(%d) = %d-%02d, want %d-%02d",
+				tt.year, m, d, tt.wantMonth, tt.wantDay)
+		}
+	}
+}
+
+func TestGermanFederalHolidays(t *testing.T) {
+	holidays := germanFederalHolidays(2026)
+
+	// Should have 11 federal holidays
+	if len(holidays) != 11 {
+		t.Fatalf("expected 11 federal holidays, got %d", len(holidays))
+	}
+
+	// Check Neujahr
+	if holidays[0].Name != "Neujahr" {
+		t.Errorf("first holiday should be Neujahr, got %s", holidays[0].Name)
+	}
+	if holidays[0].Date != time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC) {
+		t.Errorf("Neujahr should be Jan 1, got %s", holidays[0].Date)
+	}
+
+	// Check Karfreitag 2026 (Easter = Apr 5, so Good Friday = Apr 3)
+	found := false
+	for _, h := range holidays {
+		if h.Name == "Karfreitag" {
+			found = true
+			expected := time.Date(2026, 4, 3, 0, 0, 0, 0, time.UTC)
+			if h.Date != expected {
+				t.Errorf("Karfreitag 2026 should be %s, got %s", expected, h.Date)
+			}
+		}
+	}
+	if !found {
+		t.Error("Karfreitag not found in holidays")
+	}
+}
+
+func TestHolidayServiceIsNonWorkingDay(t *testing.T) {
+	svc := NewHolidayService(nil) // no DB, uses hardcoded holidays
+
+	// Saturday
+	sat := time.Date(2026, 3, 28, 0, 0, 0, 0, time.UTC)
+	if !svc.IsNonWorkingDay(sat) {
+		t.Error("Saturday should be non-working day")
+	}
+
+	// Sunday
+	sun := time.Date(2026, 3, 29, 0, 0, 0, 0, time.UTC)
+	if !svc.IsNonWorkingDay(sun) {
+		t.Error("Sunday should be non-working day")
+	}
+
+	// Regular Monday
+	mon := time.Date(2026, 3, 23, 0, 0, 0, 0, time.UTC)
+	if svc.IsNonWorkingDay(mon) {
+		t.Error("regular Monday should be a working day")
+	}
+
+	// Christmas (Friday Dec 25, 2026)
+	xmas := time.Date(2026, 12, 25, 0, 0, 0, 0, time.UTC)
+	if !svc.IsNonWorkingDay(xmas) {
+		t.Error("Christmas should be non-working day")
+	}
+
+	// New Year
+	newyear := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
+	if !svc.IsNonWorkingDay(newyear) {
+		t.Error("New Year should be non-working day")
+	}
+}
+
+func TestAdjustForNonWorkingDays(t *testing.T) {
+	svc := NewHolidayService(nil)
+
+	// Saturday -> Monday
+	sat := time.Date(2026, 3, 28, 0, 0, 0, 0, time.UTC)
+	adj, orig, adjusted := svc.AdjustForNonWorkingDays(sat)
+	if !adjusted {
+		t.Error("Saturday should be adjusted")
+	}
+	if orig != sat {
+		t.Error("original should be unchanged")
+	}
+	expected := time.Date(2026, 3, 30, 0, 0, 0, 0, time.UTC)
+	if adj != expected {
+		t.Errorf("Saturday should adjust to Monday %s, got %s", expected, adj)
+	}
+
+	// Regular Wednesday -> no adjustment
+	wed := time.Date(2026, 3, 25, 0, 0, 0, 0, time.UTC)
+	adj, _, adjusted = svc.AdjustForNonWorkingDays(wed)
+	if adjusted {
+		t.Error("Wednesday should not be adjusted")
+	}
+	if adj != wed {
+		t.Error("non-adjusted date should be unchanged")
+	}
+}