diff --git a/src/transactions/dto/transaction.dto.ts b/src/transactions/dto/transaction.dto.ts
index a8b965b..816d420 100644
--- a/src/transactions/dto/transaction.dto.ts
+++ b/src/transactions/dto/transaction.dto.ts
@@ -189,13 +189,13 @@ export enum TransactionAnalyticsGranularity {
 }
 
 export class TransactionAnalyticsQueryDto {
-  @ApiPropertyOptional({ description: 'Only include transactions created on or after this date' })
+  @ApiPropertyOptional({ description: 'Only include transactions created on or after this date. Maximum date window is 365 days when both startDate and endDate are provided.' })
   @IsOptional()
   @Type(() => Date)
   @IsDate()
   startDate?: Date;
 
-  @ApiPropertyOptional({ description: 'Only include transactions created on or before this date' })
+  @ApiPropertyOptional({ description: 'Only include transactions created on or before this date. Maximum date window is 365 days when both startDate and endDate are provided.' })
   @IsOptional()
   @Type(() => Date)
   @IsDate()
diff --git a/src/transactions/transactions.service.spec.ts b/src/transactions/transactions.service.spec.ts
index 9f11856..f6ea136 100644
--- a/src/transactions/transactions.service.spec.ts
+++ b/src/transactions/transactions.service.spec.ts
@@ -1,3 +1,4 @@
+import { BadRequestException } from '@nestjs/common';
 import { Test, TestingModule } from '@nestjs/testing';
 import { Decimal } from '@prisma/client/runtime/library';
 import { TransactionsService } from './transactions.service';
@@ -254,5 +255,15 @@ describe('TransactionsService', () => {
       expect(result.revenue).toBe(0);
       expect(result.volumeTrends).toEqual([]);
     });
+
+    it('should reject date ranges larger than 365 days', async () => {
+      const startDate = new Date('2025-01-01T00:00:00.000Z');
+      const endDate = new Date('2026-01-02T00:00:00.000Z');
+
+      await expect(
+        service.getAnalytics({ startDate, endDate, granularity: TransactionAnalyticsGranularity.MONTH }),
+      ).rejects.toThrow(BadRequestException);
+      expect(prisma.transaction.findMany).not.toHaveBeenCalled();
+    });
   });
 });
diff --git a/src/transactions/transactions.service.ts b/src/transactions/transactions.service.ts
index 57e5163..d1fb9a8 100644
--- a/src/transactions/transactions.service.ts
+++ b/src/transactions/transactions.service.ts
@@ -316,6 +316,18 @@ export class TransactionsService {
   async getAnalytics(query: TransactionAnalyticsQueryDto = {}): Promise<TransactionAnalyticsDto> {
     const where: Record<string, any> = {};
 
+    if (query.startDate && query.endDate) {
+      const maxRangeMs = 365 * 24 * 60 * 60 * 1000;
+      const durationMs = query.endDate.getTime() - query.startDate.getTime();
+
+      if (durationMs < 0) {
+        throw new BadRequestException('endDate must be on or after startDate');
+      }
+      if (durationMs > maxRangeMs) {
+        throw new BadRequestException('Date range cannot exceed 365 days');
+      }
+    }
+
     if (query.type) {
       where.type = query.type;
     }