diff --git a/src/controllers/watchAdsSessionController.ts b/src/controllers/watchAdsSessionController.ts
index 1c8376a..d18df3a 100644
--- a/src/controllers/watchAdsSessionController.ts
+++ b/src/controllers/watchAdsSessionController.ts
@@ -1,44 +1,68 @@
-  import { Request, Response } from "express";
-  import { WATCH_ADS_SESSION_STATUS } from "../models/enums/watchAds";
-  import * as WatchAdsSessionService from "../services/watchAdsSession.service";
-  import logger from "../config/loggingConfig";
-  import { IUser } from "../types";
-  
-
-  // POST /api/v1/watch-ads/session
-  export const startWatchAdsSession = async (req: Request, res: Response) => {
-    const authUser = req.currentUser as IUser;
-    if (!authUser) {
-      logger.warn("No authenticated user found when trying to start watch-ads session.");
-      return res.status(401).json({ error: "Unauthorized" });
+import { Request, Response } from "express";
+import { WATCH_ADS_SESSION_STATUS } from "../models/enums/watchAds";
+import * as WatchAdsSessionService from "../services/watchAdsSession.service";
+import logger from "../config/loggingConfig";
+import { IUser } from "../types";
+import { WatchAdsBalance } from "../models/WatchAdsBalance";
+
+// POST /api/v1/watch-ads/session
+export const startWatchAdsSession = async (req: Request, res: Response) => {
+  const authUser = req.currentUser as IUser;
+  if (!authUser) {
+    logger.warn("No authenticated user found when trying to start watch-ads session.");
+    return res.status(401).json({ error: "Unauthorized" });
+  }
+
+  try {
+    // Step 1: Check if user already has an active session
+    const activeSession = await WatchAdsSessionService.findActiveSession(authUser._id);
+    if (activeSession) {
+      return res.json(activeSession);
     }
 
-    try {
-      // Step 1: Check if user already has an active session
-      const activeSession = await WatchAdsSessionService.findActiveSession(authUser._id);
-      if (activeSession) {
-        return res.json(activeSession);
-      }
-
-      // Step 2: Create a new session
-      const newSession = await WatchAdsSessionService.createSession(authUser._id, {
-        status: WATCH_ADS_SESSION_STATUS.Running,
-        totalSegments: 20,
-        segmentSecs: 30,
-        expiresAt: new Date(Date.now() + 24 * 60 * 60 * 1000), // SESSION_TTL = 24h
-      });
-
-      return res.status(201).json(newSession);
-
-    } catch (err: any) {
-      // Handle race condition where another request created it just now
-      if (err.code === 11000) { 
-        logger.warn(`Race detected: active WatchAdsSession already exists for user ${authUser._id}`);
-        const existingSession = await WatchAdsSessionService.findActiveSession(authUser._id);
-        if (existingSession) return res.json(existingSession);
-      }
-
-      logger.error("Error starting watch-ads session", err);
-      return res.status(500).json({ error: "Internal server error" });
+    // Step 2: Create a new session
+    const newSession = await WatchAdsSessionService.createSession(authUser._id, {
+      status: WATCH_ADS_SESSION_STATUS.Running,
+      totalSegments: 20,
+      segmentSecs: 30,
+      expiresAt: new Date(Date.now() + 24 * 60 * 60 * 1000), // SESSION_TTL = 24h
+    });
+
+    return res.status(201).json(newSession);
+
+  } catch (err: any) {
+    // Handle race condition where another request created it just now
+    if (err.code === 11000) { 
+      logger.warn(`Race detected: active WatchAdsSession already exists for user ${authUser._id}`);
+      const existingSession = await WatchAdsSessionService.findActiveSession(authUser._id);
+      if (existingSession) return res.json(existingSession);
     }
-  };
+
+    logger.error("Error starting watch-ads session", err);
+    return res.status(500).json({ error: "Internal server error" });
+  }
+};
+
+// POST /api/v1/watch-ads/session/:id/segment-complete
+export const completeSegment = async (req: Request, res: Response) => {
+  const authUser = req.currentUser as IUser;
+  if (!authUser) {
+    return res.status(401).json({ error: "Unauthorized" });
+  }
+
+  try {
+    const { id } = req.params;
+    const { adId } = req.body;
+
+    const updatedSession = await WatchAdsSessionService.completeSegment(authUser._id, id, adId);
+    if (!updatedSession) {
+      return res.status(404).json({ error: "Session not found or expired" });
+    }
+
+    return res.json(updatedSession);
+
+  } catch (err: any) {
+    logger.error("Error completing watch-ads segment", err);
+    return res.status(500).json({ error: "Internal server error" });
+  }
+};
diff --git a/src/routes/watchAds.routes.ts b/src/routes/watchAds.routes.ts
index d92c39d..044e175 100644
--- a/src/routes/watchAds.routes.ts
+++ b/src/routes/watchAds.routes.ts
@@ -1,5 +1,5 @@
 import { Router } from 'express';
-import { startWatchAdsSession } from '../controllers/watchAdsSessionController';
+import { startWatchAdsSession, completeSegment } from '../controllers/watchAdsSessionController';
 import { verifyToken } from '../middlewares/verifyToken';
 
 const router = Router();
@@ -7,4 +7,6 @@ const router = Router();
 // start/resume endpoint
 router.post('/watch-ads/session', verifyToken, startWatchAdsSession);
 
+router.post('/watch-ads/session/:id/segment-complete', verifyToken, completeSegment);
+
 export default router;
\ No newline at end of file
diff --git a/src/services/watchAdsSession.service.ts b/src/services/watchAdsSession.service.ts
index 8edd389..f91c55c 100644
--- a/src/services/watchAdsSession.service.ts
+++ b/src/services/watchAdsSession.service.ts
@@ -1,6 +1,7 @@
 import { Types } from 'mongoose';
 import { WatchAdsSession } from '../models/WatchAdsSession';
 import { WATCH_ADS_SESSION_STATUS } from '../models/enums/watchAds';
+import { WatchAdsBalance } from '../models/WatchAdsBalance';
 
 type CreateOpts = {
   status?: string;          // should be WATCH_ADS_SESSION_STATUS.Running
@@ -28,12 +29,9 @@ export async function createSession(userId: Types.ObjectId, opts: CreateOpts = {
   status = WATCH_ADS_SESSION_STATUS.Running,
   totalSegments = opts.totalSegments ?? 20,
   segmentSecs = opts.segmentSecs ?? 30,
-  expiresAt = opts.expiresAt ?? new Date(
-    nowMs + (opts.totalSegments ?? 20) * (opts.segmentSecs ?? 30) * 1000 + 10 * 60 * 1000
-  ),
+  expiresAt = opts.expiresAt ?? new Date(nowMs + 24 * 60 * 60 * 1000),
 } = opts;
 
-
   // Validation
   if (totalSegments <= 0 || segmentSecs <= 0) {
     throw new Error("Invalid session parameters: totalSegments and segmentSecs must be greater than 0");
@@ -77,7 +75,7 @@ export async function createSession(userId: Types.ObjectId, opts: CreateOpts = {
     }
   }
 
-  // If we hit here, repeated collisions — just return the active one if any
+  // If we hit repeated collisions — just return the active one if any
   return WatchAdsSession.findOne({
     userId,
     status: WATCH_ADS_SESSION_STATUS.Running,
@@ -85,3 +83,38 @@ export async function createSession(userId: Types.ObjectId, opts: CreateOpts = {
   }).lean();
 }
 
+export async function completeSegment(userId: Types.ObjectId, sessionId: string, adId: string) {
+  // 1. Find active session
+  const session = await WatchAdsSession.findOne({
+    _id: sessionId,
+    userId,
+    status: WATCH_ADS_SESSION_STATUS.Running,
+  });
+  if (!session) return null;
+
+  // 2. Increment session progress
+  session.completedSegments += 1;
+  session.earnedSecs += session.segmentSecs;
+
+  if (session.completedSegments >= session.totalSegments) {
+    session.status = WATCH_ADS_SESSION_STATUS.Completed;
+    session.endedAt = new Date();
+  }
+
+  await session.save();
+
+  // 3. Increment or create balance
+  await WatchAdsBalance.findOneAndUpdate(
+    { userId },
+    {
+      $inc: {
+        availableSecs: session.segmentSecs,
+        lifetimeEarnedSecs: session.segmentSecs,
+      },
+    },
+    { upsert: true, new: true }
+  );
+
+  // 4. Return updated session
+  return session.toObject();
+}