diff --git a/backend/analytics/__tests__/cohortAnalyticsRouter.test.ts b/backend/analytics/__tests__/cohortAnalyticsRouter.test.ts
new file mode 100644
index 00000000..9fc23555
--- /dev/null
+++ b/backend/analytics/__tests__/cohortAnalyticsRouter.test.ts
@@ -0,0 +1,321 @@
+/**
+ * Unit tests for cohortAnalyticsRouter.ts
+ *
+ * Covers:
+ *  - GET /analytics/cohorts           → cohort table (monthly & weekly)
+ *  - GET /analytics/cohorts/retention → Day 1/7/30/60/90 retention curve
+ *  - GET /analytics/cohorts/churn     → revenue churn vs logo churn
+ *  - GET /analytics/cohorts/export    → CSV and PDF download
+ *  - GET /analytics/cohorts/mrr       → MRR/ARR/ARPU/LTV summary
+ *  - POST /analytics/cohorts/subscribers → upsert subscriber record
+ *  - Validation: missing merchantId → 400
+ *  - Non-GET to read endpoint → 405
+ *  - Unmatched sub-path → returns false
+ */
+
+import { describe, it, expect, beforeEach } from '@jest/globals';
+import type http from 'node:http';
+import { cohortAnalyticsRouter } from '../cohortAnalyticsRouter';
+import { subscriberRecordRepository } from '../../services/analytics/subscriberRecordRepository';
+import type { SubscriberRecord } from '../../../src/types/cohortAnalytics';
+
+// ─── Minimal mock helpers ─────────────────────────────────────────────────────
+
+type MockRes = http.ServerResponse & {
+  statusCode: number;
+  body: string;
+  headers: Record<string, string>;
+  json(): unknown;
+};
+
+function makeRes(): MockRes {
+  const headers: Record<string, string> = {};
+  let statusCode = 0;
+  let body = '';
+  return {
+    writeHead(code: number, hdrs?: Record<string, string>) {
+      statusCode = code;
+      Object.assign(headers, hdrs ?? {});
+    },
+    end(data?: unknown) { body = data ? String(data) : ''; },
+    get statusCode() { return statusCode; },
+    get body() { return body; },
+    get headers() { return headers; },
+    json() { return JSON.parse(body); },
+  } as unknown as MockRes;
+}
+
+function makeReq(method: string, url: string, bodyObj?: unknown): http.IncomingMessage {
+  const bodyStr = bodyObj ? JSON.stringify(bodyObj) : '';
+  const chunks = bodyStr ? [Buffer.from(bodyStr)] : [];
+  const req = {
+    method,
+    url,
+    headers: { host: 'localhost' },
+    on(event: string, handler: (chunk?: unknown) => void) {
+      if (event === 'data') for (const c of chunks) handler(c);
+      if (event === 'end') handler();
+      return req;
+    },
+  } as unknown as http.IncomingMessage;
+  return req;
+}
+
+// ─── Fixtures ─────────────────────────────────────────────────────────────────
+
+const NOW = Date.now();
+const TWO_MONTHS_AGO = NOW - 60 * 24 * 60 * 60 * 1000;
+const ONE_MONTH_AGO  = NOW - 30 * 24 * 60 * 60 * 1000;
+const MERCHANT = 'merch_test';
+
+function makeRecord(overrides: Partial<SubscriberRecord> = {}): SubscriberRecord {
+  return {
+    subscriberId: `sub_${Math.random().toString(36).slice(2)}`,
+    merchantId: MERCHANT,
+    planId: 'plan_basic',
+    planName: 'Basic',
+    signupAt: TWO_MONTHS_AGO,
+    mrr: 29,
+    ...overrides,
+  };
+}
+
+beforeEach(() => {
+  subscriberRecordRepository.seed(MERCHANT, [
+    makeRecord({ signupAt: TWO_MONTHS_AGO }),
+    makeRecord({ signupAt: TWO_MONTHS_AGO }),
+    makeRecord({
+      signupAt: ONE_MONTH_AGO,
+      churnedAt: ONE_MONTH_AGO + 5 * 24 * 60 * 60 * 1000,
+    }),
+  ]);
+});
+
+// ─── Non-matching paths ───────────────────────────────────────────────────────
+
+describe('cohortAnalyticsRouter — non-matching paths', () => {
+  it('returns false for paths outside /analytics/cohorts', async () => {
+    const res = makeRes();
+    const handled = await cohortAnalyticsRouter(makeReq('GET', '/other'), res, '/other');
+    expect(handled).toBe(false);
+  });
+});
+
+// ─── Validation ───────────────────────────────────────────────────────────────
+
+describe('cohortAnalyticsRouter — validation', () => {
+  it('returns 400 when merchantId missing', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(makeReq('GET', '/analytics/cohorts'), res, '/analytics/cohorts');
+    expect(res.statusCode).toBe(400);
+    expect((res.json() as { success: boolean }).success).toBe(false);
+  });
+
+  it('returns 405 for non-GET to /analytics/cohorts', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('DELETE', `/analytics/cohorts?merchantId=${MERCHANT}`),
+      res,
+      '/analytics/cohorts'
+    );
+    expect(res.statusCode).toBe(405);
+  });
+});
+
+// ─── GET /analytics/cohorts (cohort table) ────────────────────────────────────
+
+describe('GET /analytics/cohorts', () => {
+  it('returns a cohort table array', async () => {
+    const res = makeRes();
+    const handled = await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts?merchantId=${MERCHANT}`),
+      res, '/analytics/cohorts'
+    );
+    expect(handled).toBe(true);
+    expect(res.statusCode).toBe(200);
+    const body = res.json() as { success: boolean; data: unknown[] };
+    expect(body.success).toBe(true);
+    expect(Array.isArray(body.data)).toBe(true);
+    expect(body.data.length).toBeGreaterThan(0);
+  });
+
+  it('buckets have required fields', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts?merchantId=${MERCHANT}`),
+      res, '/analytics/cohorts'
+    );
+    const bucket = (res.json() as { data: Array<Record<string, unknown>> }).data[0]!;
+    expect(bucket).toHaveProperty('cohortKey');
+    expect(bucket).toHaveProperty('size');
+    expect(bucket).toHaveProperty('activeCount');
+    expect(bucket).toHaveProperty('retentionRate');
+  });
+
+  it('accepts granularity=week and returns week-keyed buckets', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts?merchantId=${MERCHANT}&granularity=week`),
+      res, '/analytics/cohorts'
+    );
+    expect(res.statusCode).toBe(200);
+    const buckets = (res.json() as { data: Array<{ granularity: string }> }).data;
+    expect(buckets.every((b) => b.granularity === 'week')).toBe(true);
+  });
+});
+
+// ─── GET /analytics/cohorts/retention ────────────────────────────────────────
+
+describe('GET /analytics/cohorts/retention', () => {
+  it('returns an array of retention curve points', async () => {
+    const res = makeRes();
+    const handled = await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/retention?merchantId=${MERCHANT}`),
+      res, '/analytics/cohorts/retention'
+    );
+    expect(handled).toBe(true);
+    expect(res.statusCode).toBe(200);
+    const body = res.json() as { success: boolean; data: unknown[] };
+    expect(body.success).toBe(true);
+    expect(Array.isArray(body.data)).toBe(true);
+  });
+
+  it('each point has day, retainedCount, cohortSize, retentionRate', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/retention?merchantId=${MERCHANT}`),
+      res, '/analytics/cohorts/retention'
+    );
+    const points = (res.json() as { data: Array<Record<string, unknown>> }).data;
+    if (points.length > 0) {
+      expect(points[0]).toHaveProperty('day');
+      expect(points[0]).toHaveProperty('retainedCount');
+      expect(points[0]).toHaveProperty('cohortSize');
+      expect(points[0]).toHaveProperty('retentionRate');
+    }
+  });
+});
+
+// ─── GET /analytics/cohorts/churn ────────────────────────────────────────────
+
+describe('GET /analytics/cohorts/churn', () => {
+  it('returns churn breakdown with success=true', async () => {
+    const res = makeRes();
+    const handled = await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/churn?merchantId=${MERCHANT}&from=${TWO_MONTHS_AGO}&to=${NOW}`),
+      res, '/analytics/cohorts/churn'
+    );
+    expect(handled).toBe(true);
+    expect(res.statusCode).toBe(200);
+    expect((res.json() as { success: boolean }).success).toBe(true);
+  });
+
+  it('defaults from/to when params omitted', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/churn?merchantId=${MERCHANT}`),
+      res, '/analytics/cohorts/churn'
+    );
+    expect(res.statusCode).toBe(200);
+  });
+});
+
+// ─── GET /analytics/cohorts/mrr ───────────────────────────────────────────────
+
+describe('GET /analytics/cohorts/mrr', () => {
+  it('returns MRR/ARR/ARPU/LTV summary', async () => {
+    const res = makeRes();
+    const handled = await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/mrr?merchantId=${MERCHANT}`),
+      res, '/analytics/cohorts/mrr'
+    );
+    expect(handled).toBe(true);
+    expect(res.statusCode).toBe(200);
+    const data = (res.json() as { data: Record<string, unknown> }).data;
+    expect(data).toHaveProperty('mrr');
+    expect(data).toHaveProperty('arr');
+    expect(data).toHaveProperty('arpu');
+    expect(data).toHaveProperty('ltv');
+    expect(data).toHaveProperty('activeCount');
+    expect(data).toHaveProperty('subscriberCount');
+  });
+
+  it('mrr is positive for seeded data', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/mrr?merchantId=${MERCHANT}`),
+      res, '/analytics/cohorts/mrr'
+    );
+    const data = (res.json() as { data: { mrr: number } }).data;
+    expect(data.mrr).toBeGreaterThan(0);
+  });
+});
+
+// ─── GET /analytics/cohorts/export ───────────────────────────────────────────
+
+describe('GET /analytics/cohorts/export', () => {
+  it('CSV: returns 200 with text/csv Content-Type and Content-Disposition', async () => {
+    const res = makeRes();
+    const handled = await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/export?merchantId=${MERCHANT}&granularity=month&format=csv`),
+      res, '/analytics/cohorts/export'
+    );
+    expect(handled).toBe(true);
+    expect(res.statusCode).toBe(200);
+    expect(res.headers['Content-Type']).toContain('text/csv');
+    expect(res.headers['Content-Disposition']).toContain('attachment');
+    expect(res.headers['Content-Disposition']).toContain('.csv');
+  });
+
+  it('CSV body contains expected column headers', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/export?merchantId=${MERCHANT}&format=csv`),
+      res, '/analytics/cohorts/export'
+    );
+    expect(res.body).toContain('cohort');
+    expect(res.body).toContain('retentionRate');
+  });
+
+  it('PDF: returns 200 with application/pdf Content-Type', async () => {
+    const res = makeRes();
+    await cohortAnalyticsRouter(
+      makeReq('GET', `/analytics/cohorts/export?merchantId=${MERCHANT}&format=pdf`),
+      res, '/analytics/cohorts/export'
+    );
+    expect(res.statusCode).toBe(200);
+    expect(res.headers['Content-Type']).toContain('application/pdf');
+  });
+});
+
+// ─── POST /analytics/cohorts/subscribers ─────────────────────────────────────
+
+describe('POST /analytics/cohorts/subscribers', () => {
+  it('upserts a record and returns success', async () => {
+    const record: SubscriberRecord = makeRecord({ subscriberId: 'sub_new', merchantId: 'merch_new' });
+    const res = makeRes();
+    const handled = await cohortAnalyticsRouter(
+      makeReq('POST', '/analytics/cohorts/subscribers', record),
+      res, '/analytics/cohorts/subscribers'
+    );
+    expect(handled).toBe(true);
+    expect(res.statusCode).toBe(200);
+    expect((res.json() as { success: boolean }).success).toBe(true);
+  });
+
+  it('returns 400 for invalid JSON body', async () => {
+    const req = {
+      method: 'POST',
+      url: '/analytics/cohorts/subscribers',
+      headers: { host: 'localhost' },
+      on(event: string, handler: (chunk?: unknown) => void) {
+        if (event === 'data') handler(Buffer.from('{bad json'));
+        if (event === 'end') handler();
+        return req;
+      },
+    } as unknown as http.IncomingMessage;
+    const res = makeRes();
+    await cohortAnalyticsRouter(req, res, '/analytics/cohorts/subscribers');
+    expect(res.statusCode).toBe(400);
+  });
+});
diff --git a/backend/analytics/cohortAnalyticsRouter.ts b/backend/analytics/cohortAnalyticsRouter.ts
new file mode 100644
index 00000000..c383c14f
--- /dev/null
+++ b/backend/analytics/cohortAnalyticsRouter.ts
@@ -0,0 +1,150 @@
+/**
+ * cohortAnalyticsRouter
+ *
+ * Plain Node.js HTTP handler for cohort retention and churn analytics.
+ * Mounts under `/analytics/cohorts` in server.ts.
+ *
+ * Routes
+ * ──────
+ *   GET  /analytics/cohorts?merchantId=…&granularity=month|week
+ *        Cohort table grouped by signup period
+ *
+ *   GET  /analytics/cohorts/retention?merchantId=…
+ *        Day 1/7/30/60/90 retention curve
+ *
+ *   GET  /analytics/cohorts/churn?merchantId=…&from=<epochMs>&to=<epochMs>
+ *        Revenue churn vs logo churn breakdown for a period
+ *
+ *   GET  /analytics/cohorts/export?merchantId=…&granularity=month|week&format=csv|pdf
+ *        Downloadable cohort table (CSV or PDF)
+ *
+ *   GET  /analytics/cohorts/mrr?merchantId=…
+ *        MRR / ARR / ARPU / LTV summary
+ *
+ *   POST /analytics/cohorts/subscribers
+ *        Upsert a subscriber record (seed data into the in-memory store)
+ *        Body: SubscriberRecord (JSON)
+ *
+ * All JSON responses follow { success, data } | { success, error }.
+ * Export responses stream file bytes with Content-Disposition for download.
+ */
+
+import type http from 'node:http';
+import { URL } from 'node:url';
+import { analyticsDashboardApi } from '../services/analytics/analyticsDashboardApi';
+import { subscriberRecordRepository } from '../services/analytics/subscriberRecordRepository';
+import type { CohortGranularity, AnalyticsExportFormat } from '../../src/types/cohortAnalytics';
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+function sendJson(res: http.ServerResponse, status: number, body: unknown): void {
+  res.writeHead(status, { 'Content-Type': 'application/json' });
+  res.end(JSON.stringify(body));
+}
+
+async function readJsonBody(req: http.IncomingMessage, maxBytes = 64_000): Promise<unknown> {
+  return new Promise<unknown>((resolve, reject) => {
+    const chunks: Buffer[] = [];
+    let total = 0;
+    req.on('data', (chunk: Buffer) => {
+      total += chunk.length;
+      if (total > maxBytes) { reject(new Error('Request body too large')); return; }
+      chunks.push(chunk);
+    });
+    req.on('end', () => {
+      try { resolve(JSON.parse(Buffer.concat(chunks).toString('utf8'))); }
+      catch { reject(new Error('Invalid JSON body')); }
+    });
+    req.on('error', reject);
+  });
+}
+
+// ─── Router ───────────────────────────────────────────────────────────────────
+
+const PREFIX = '/analytics/cohorts';
+
+export async function cohortAnalyticsRouter(
+  req: http.IncomingMessage,
+  res: http.ServerResponse,
+  pathname: string
+): Promise<boolean> {
+  if (!pathname.startsWith(PREFIX)) return false;
+
+  const method = req.method ?? 'GET';
+  const url = new URL(req.url ?? '/', `http://${req.headers.host ?? 'localhost'}`);
+  const merchantId = url.searchParams.get('merchantId') ?? '';
+  const subPath = pathname.slice(PREFIX.length); // e.g. '', '/retention', '/churn', ...
+
+  // ── POST /analytics/cohorts/subscribers  (seed/upsert a subscriber record) ─
+  if (subPath === '/subscribers' && method === 'POST') {
+    try {
+      const body = await readJsonBody(req) as Record<string, unknown>;
+      subscriberRecordRepository.upsert(body as never);
+      sendJson(res, 200, { success: true, data: { upserted: true } });
+    } catch (err) {
+      sendJson(res, 400, { success: false, error: err instanceof Error ? err.message : String(err) });
+    }
+    return true;
+  }
+
+  if (method !== 'GET') {
+    sendJson(res, 405, { success: false, error: 'Method not allowed' });
+    return true;
+  }
+
+  if (!merchantId) {
+    sendJson(res, 400, { success: false, error: 'merchantId query parameter is required' });
+    return true;
+  }
+
+  // ── GET /analytics/cohorts/retention ──────────────────────────────────────
+  if (subPath === '/retention') {
+    const result = analyticsDashboardApi.getRetentionCurve(merchantId);
+    sendJson(res, result.success ? 200 : 500, result);
+    return true;
+  }
+
+  // ── GET /analytics/cohorts/churn ──────────────────────────────────────────
+  if (subPath === '/churn') {
+    const from = parseInt(url.searchParams.get('from') ?? '0', 10);
+    const to = parseInt(url.searchParams.get('to') ?? String(Date.now()), 10);
+    const result = analyticsDashboardApi.getChurnBreakdown(merchantId, from, to);
+    sendJson(res, result.success ? 200 : 500, result);
+    return true;
+  }
+
+  // ── GET /analytics/cohorts/export ─────────────────────────────────────────
+  if (subPath === '/export') {
+    const granularity = (url.searchParams.get('granularity') ?? 'month') as CohortGranularity;
+    const format = (url.searchParams.get('format') ?? 'csv') as AnalyticsExportFormat;
+    const result = analyticsDashboardApi.exportCohortReport(merchantId, granularity, format);
+    if (!result.success || !result.data) {
+      sendJson(res, 500, result);
+      return true;
+    }
+    const { filename, contentType, body } = result.data;
+    res.writeHead(200, {
+      'Content-Type': contentType,
+      'Content-Disposition': `attachment; filename="${filename}"`,
+    });
+    res.end(body);
+    return true;
+  }
+
+  // ── GET /analytics/cohorts/mrr ────────────────────────────────────────────
+  if (subPath === '/mrr') {
+    const result = analyticsDashboardApi.getMrrArrReport(merchantId);
+    sendJson(res, result.success ? 200 : 500, result);
+    return true;
+  }
+
+  // ── GET /analytics/cohorts  (cohort table — default) ──────────────────────
+  if (subPath === '' || subPath === '/') {
+    const granularity = (url.searchParams.get('granularity') ?? 'month') as CohortGranularity;
+    const result = analyticsDashboardApi.getCohortTable(merchantId, granularity);
+    sendJson(res, result.success ? 200 : 500, result);
+    return true;
+  }
+
+  return false;
+}