diff --git a/__tests__/api/bikes.test.ts b/__tests__/api/bikes.test.ts
index a74b59e..d9e5ef0 100644
--- a/__tests__/api/bikes.test.ts
+++ b/__tests__/api/bikes.test.ts
@@ -93,6 +93,50 @@ describe('Bikes API', () => {
 
       expect(bike.name).toBe('My Test Bike')
     })
+
+    it('should create bike with purchaseDate in YYYY-MM-DD format', async () => {
+      const bikeData = {
+        name: 'Bike with Date',
+        purchaseDate: new Date('2024-01-15T00:00:00.000Z'),
+      }
+
+      const bike = await prisma.bike.create({
+        data: bikeData,
+      })
+
+      expect(bike).toBeDefined()
+      expect(bike.purchaseDate).toBeInstanceOf(Date)
+      expect(bike.purchaseDate?.toISOString().split('T')[0]).toBe('2024-01-15')
+    })
+
+    it('should create bike with purchaseDate', async () => {
+      const purchaseDate = new Date('2024-03-20')
+      const bikeData = {
+        name: 'Bike with Purchase Date',
+        purchaseDate: purchaseDate,
+      }
+
+      const bike = await prisma.bike.create({
+        data: bikeData,
+      })
+
+      expect(bike).toBeDefined()
+      expect(bike.purchaseDate).toBeInstanceOf(Date)
+      expect(bike.purchaseDate?.getTime()).toBe(purchaseDate.getTime())
+    })
+
+    it('should create bike without purchaseDate', async () => {
+      const bikeData = {
+        name: 'Bike without Date',
+      }
+
+      const bike = await prisma.bike.create({
+        data: bikeData,
+      })
+
+      expect(bike).toBeDefined()
+      expect(bike.purchaseDate).toBeNull()
+    })
   })
 
   describe('GET /api/bikes', () => {
diff --git a/__tests__/lib/validations.test.ts b/__tests__/lib/validations.test.ts
index 4e6fd7b..b712821 100644
--- a/__tests__/lib/validations.test.ts
+++ b/__tests__/lib/validations.test.ts
@@ -173,6 +173,85 @@ describe('Validation Schemas', () => {
         expect(result.data.notes).toBeUndefined()
       }
     })
+
+    it('should accept purchaseDate in YYYY-MM-DD format', () => {
+      // The schema accepts any string and transforms it to Date
+      const validData = {
+        name: 'Test Bike',
+        purchaseDate: '2024-01-15',
+      }
+
+      const result = bikeSchema.safeParse(validData)
+      if (!result.success) {
+        // Debug: show what went wrong
+        console.log('Validation failed:', JSON.stringify(result.error.errors, null, 2))
+      }
+      expect(result.success).toBe(true)
+      if (result.success) {
+        // Transform converts string to Date
+        expect(result.data.purchaseDate).toBeDefined()
+        if (result.data.purchaseDate) {
+          expect(result.data.purchaseDate).toBeInstanceOf(Date)
+          expect(result.data.purchaseDate.toISOString().split('T')[0]).toBe('2024-01-15')
+        }
+      }
+    })
+
+    it('should accept purchaseDate in ISO datetime format', () => {
+      const validData = {
+        name: 'Test Bike',
+        purchaseDate: '2024-01-15T10:30:00.000Z',
+      }
+
+      const result = bikeSchema.safeParse(validData)
+      expect(result.success).toBe(true)
+      if (result.success) {
+        // The transform converts it to Date, but Zod might return the string
+        // Let's check if it's a Date or a valid date string
+        expect(result.data.purchaseDate).toBeDefined()
+        if (result.data.purchaseDate instanceof Date) {
+          expect(result.data.purchaseDate).toBeInstanceOf(Date)
+        } else {
+          // If it's still a string, it should be parseable
+          expect(new Date(result.data.purchaseDate as string)).toBeInstanceOf(Date)
+        }
+      }
+    })
+
+    it('should accept purchaseDate as Date object', () => {
+      const validData = {
+        name: 'Test Bike',
+        purchaseDate: new Date('2024-01-15'),
+      }
+
+      const result = bikeSchema.safeParse(validData)
+      expect(result.success).toBe(true)
+      if (result.success) {
+        expect(result.data.purchaseDate).toBeInstanceOf(Date)
+      }
+    })
+
+    it('should accept bike without purchaseDate', () => {
+      const validData = {
+        name: 'Test Bike',
+      }
+
+      const result = bikeSchema.safeParse(validData)
+      expect(result.success).toBe(true)
+      if (result.success) {
+        expect(result.data.purchaseDate).toBeUndefined()
+      }
+    })
+
+    it('should reject invalid purchaseDate format', () => {
+      const invalidData = {
+        name: 'Test Bike',
+        purchaseDate: 'invalid-date',
+      }
+
+      const result = bikeSchema.safeParse(invalidData)
+      expect(result.success).toBe(false)
+    })
   })
 
   describe('wearPartSchema', () => {
diff --git a/app/api/bikes/[id]/route.ts b/app/api/bikes/[id]/route.ts
index f89cdcd..08a22ef 100644
--- a/app/api/bikes/[id]/route.ts
+++ b/app/api/bikes/[id]/route.ts
@@ -56,9 +56,7 @@ export async function PUT(
         name: validatedData.name,
         brand: validatedData.brand,
         model: validatedData.model,
-        purchaseDate: validatedData.purchaseDate
-          ? new Date(validatedData.purchaseDate)
-          : null,
+        purchaseDate: validatedData.purchaseDate || null,
         notes: validatedData.notes,
       },
     })
diff --git a/app/api/bikes/route.ts b/app/api/bikes/route.ts
index 110a120..5f259eb 100644
--- a/app/api/bikes/route.ts
+++ b/app/api/bikes/route.ts
@@ -41,9 +41,7 @@ export async function POST(request: NextRequest) {
         name: validatedData.name,
         brand: validatedData.brand,
         model: validatedData.model,
-        purchaseDate: validatedData.purchaseDate
-          ? new Date(validatedData.purchaseDate)
-          : null,
+        purchaseDate: validatedData.purchaseDate || null,
         notes: validatedData.notes,
       },
     })
diff --git a/lib/validations.ts b/lib/validations.ts
index 98d59a5..997d623 100644
--- a/lib/validations.ts
+++ b/lib/validations.ts
@@ -43,7 +43,29 @@ export const bikeSchema = z.object({
     .min(1, 'Name darf nicht nur aus Leerzeichen bestehen'),
   brand: z.string().optional().transform((val) => val?.trim() || undefined),
   model: z.string().optional().transform((val) => val?.trim() || undefined),
-  purchaseDate: z.string().datetime().optional().or(z.date().optional()),
+  purchaseDate: z
+    .union([z.date(), z.string()])
+    .optional()
+    .transform((val) => {
+      if (!val || val === undefined) return undefined
+      if (val instanceof Date) {
+        return isNaN(val.getTime()) ? undefined : val
+      }
+      if (typeof val === 'string') {
+        // Handle YYYY-MM-DD format (from HTML date input)
+        if (/^\d{4}-\d{2}-\d{2}$/.test(val)) {
+          const date = new Date(val + 'T00:00:00.000Z')
+          return isNaN(date.getTime()) ? undefined : date
+        }
+        // Handle ISO datetime format or any other parseable date string
+        const date = new Date(val)
+        return isNaN(date.getTime()) ? undefined : date
+      }
+      return undefined
+    })
+    .refine((val) => val === undefined || val instanceof Date, {
+      message: 'Ungültiges Datumsformat',
+    }),
   notes: z.string().optional().transform((val) => val?.trim() || undefined),
 })