diff --git a/Tethering/src/com/android/networkstack/tethering/metrics/TetheringMetrics.java b/Tethering/src/com/android/networkstack/tethering/metrics/TetheringMetrics.java
index fc50faf..32c1410 100644
--- a/Tethering/src/com/android/networkstack/tethering/metrics/TetheringMetrics.java
+++ b/Tethering/src/com/android/networkstack/tethering/metrics/TetheringMetrics.java
@@ -111,7 +111,11 @@
     private final SparseArray<NetworkTetheringReported.Builder> mBuilderMap = new SparseArray<>();
     private final SparseArray<Long> mDownstreamStartTime = new SparseArray<Long>();
     private final ArrayList<RecordUpstreamEvent> mUpstreamEventList = new ArrayList<>();
-    private final ArrayMap<UpstreamType, DataUsage> mUpstreamUsageBaseline = new ArrayMap<>();
+    // Store the last reported data usage for each upstream type to be used for calculating the
+    // usage delta. The keys are the upstream types, and the values are the tethering UID data
+    // usage for the corresponding types. Retrieve the baseline data usage when tethering is
+    // enabled, update it when the upstream changes, and clear it when tethering is disabled.
+    private final ArrayMap<UpstreamType, DataUsage> mLastReportedUpstreamUsage = new ArrayMap<>();
     private final Context mContext;
     private final Dependencies mDependencies;
     private final NetworkStatsManager mNetworkStatsManager;
@@ -282,22 +286,33 @@
      * Calculates the data usage difference between the current and previous usage for the
      * specified upstream type.
      *
+     * Note: This must be called before updating mCurrentUpstream when changing the upstream.
+     *
      * @return A DataUsage object containing the calculated difference in transmitted (tx) and
      *         received (rx) bytes.
      */
     private DataUsage calculateDataUsageDelta(@Nullable UpstreamType upstream) {
-        if (upstream != null && mDependencies.isUpstreamDataUsageMetricsEnabled(mContext)
-                && isUsageSupportedForUpstreamType(upstream)) {
-            final DataUsage oldUsage = mUpstreamUsageBaseline.getOrDefault(upstream, EMPTY);
-            if (oldUsage.equals(EMPTY)) {
-                Log.d(TAG, "No usage baseline for the upstream=" + upstream);
-                return EMPTY;
-            }
-            // TODO(b/352537247): Fix data usage which might be incorrect if the device uses
-            //  tethering with the same upstream for over 15 days.
-            return DataUsage.subtract(getCurrentDataUsageForUpstreamType(upstream), oldUsage);
+        if (!mDependencies.isUpstreamDataUsageMetricsEnabled(mContext)) {
+            return EMPTY;
         }
-        return EMPTY;
+
+        if (upstream == null || !isUsageSupportedForUpstreamType(upstream)) {
+            return EMPTY;
+        }
+
+        final DataUsage oldUsage = mLastReportedUpstreamUsage.getOrDefault(upstream, EMPTY);
+        if (oldUsage.equals(EMPTY)) {
+            Log.d(TAG, "No usage baseline for the upstream=" + upstream);
+            return EMPTY;
+        }
+        // TODO(b/370724247): Fix data usage which might be incorrect if the device uses
+        //  tethering with the same upstream for over 15 days.
+        // Need to refresh the baseline usage data. If the network switches back to Wi-Fi after
+        // using cellular data (Wi-Fi -> Cellular -> Wi-Fi), the old baseline might be
+        // inaccurate, leading to incorrect delta calculations.
+        final DataUsage newUsage = getCurrentDataUsageForUpstreamType(upstream);
+        mLastReportedUpstreamUsage.put(upstream, newUsage);
+        return DataUsage.subtract(newUsage, oldUsage);
     }
 
     /**
@@ -444,25 +459,29 @@
     }
 
     private void handleInitUpstreamUsageBaseline() {
-        if (!(mDependencies.isUpstreamDataUsageMetricsEnabled(mContext)
-                && mUpstreamUsageBaseline.isEmpty())) {
+        if (!mDependencies.isUpstreamDataUsageMetricsEnabled(mContext)) {
+            return;
+        }
+
+        if (!mLastReportedUpstreamUsage.isEmpty()) {
+            Log.wtf(TAG, "The upstream usage baseline has been initialed.");
             return;
         }
 
         for (UpstreamType type : UpstreamType.values()) {
             if (!isUsageSupportedForUpstreamType(type)) continue;
-            mUpstreamUsageBaseline.put(type, getCurrentDataUsageForUpstreamType(type));
+            mLastReportedUpstreamUsage.put(type, getCurrentDataUsageForUpstreamType(type));
         }
     }
 
     @VisibleForTesting
     @NonNull
-    DataUsage getDataUsageFromUpstreamType(@NonNull UpstreamType type) {
+    DataUsage getLastReportedUsageFromUpstreamType(@NonNull UpstreamType type) {
         if (mHandler.getLooper().getThread() != Thread.currentThread()) {
             throw new IllegalStateException(
                     "Not running on Handler thread: " + Thread.currentThread().getName());
         }
-        return mUpstreamUsageBaseline.getOrDefault(type, EMPTY);
+        return mLastReportedUpstreamUsage.getOrDefault(type, EMPTY);
     }
 
 
@@ -497,7 +516,7 @@
         mUpstreamEventList.clear();
         mCurrentUpstream = null;
         mCurrentUpStreamStartTime = 0L;
-        mUpstreamUsageBaseline.clear();
+        mLastReportedUpstreamUsage.clear();
     }
 
     private DownstreamType downstreamTypeToEnum(final int ifaceType) {
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/metrics/TetheringMetricsTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/metrics/TetheringMetricsTest.java
index 34689bc..f736dbf 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/metrics/TetheringMetricsTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/metrics/TetheringMetricsTest.java
@@ -498,7 +498,7 @@
     private void verifyEmptyUsageForAllUpstreamTypes() {
         mHandler.post(() -> {
             for (UpstreamType type : UpstreamType.values()) {
-                assertEquals(EMPTY, mTetheringMetrics.getDataUsageFromUpstreamType(type));
+                assertEquals(EMPTY, mTetheringMetrics.getLastReportedUsageFromUpstreamType(type));
             }
         });
         HandlerUtils.waitForIdle(mHandler, DEFAULT_TIMEOUT);
@@ -555,7 +555,8 @@
 
         mHandler.post(() -> {
             for (UpstreamType type : UpstreamType.values()) {
-                final DataUsage dataUsage = mTetheringMetrics.getDataUsageFromUpstreamType(type);
+                final DataUsage dataUsage =
+                        mTetheringMetrics.getLastReportedUsageFromUpstreamType(type);
                 if (TetheringMetrics.isUsageSupportedForUpstreamType(type)) {
                     assertEquals(mMockUpstreamUsageBaseline.get(type), dataUsage);
                 } else {
@@ -610,12 +611,21 @@
         incrementCurrentTime(cellDuration);
         updateUpstreamDataUsage(UT_CELLULAR, cellUsageDiff);
 
+        // Change the upstream back to Wi-FI and update the data usage
+        runAndWaitForIdle(() ->
+                mTetheringMetrics.maybeUpdateUpstreamType(buildUpstreamState(TRANSPORT_WIFI)));
+        final long wifiDuration2 = 50 * SECOND_IN_MILLIS;
+        final long wifiUsageDiff2 = 1000L;
+        incrementCurrentTime(wifiDuration2);
+        updateUpstreamDataUsage(UT_WIFI, wifiUsageDiff2);
+
         // Stop tethering and verify that the data usage is uploaded.
         updateErrorAndSendReport(TETHERING_WIFI, TETHER_ERROR_NO_ERROR);
         UpstreamEvents.Builder upstreamEvents = UpstreamEvents.newBuilder();
         addUpstreamEvent(upstreamEvents, UT_WIFI, wifiDuration, wifiUsageDiff, wifiUsageDiff);
         addUpstreamEvent(upstreamEvents, UT_BLUETOOTH, bluetoothDuration, btUsageDiff, btUsageDiff);
         addUpstreamEvent(upstreamEvents, UT_CELLULAR, cellDuration, cellUsageDiff, cellUsageDiff);
+        addUpstreamEvent(upstreamEvents, UT_WIFI, wifiDuration2, wifiUsageDiff2, wifiUsageDiff2);
         verifyReport(DownstreamType.DS_TETHERING_WIFI, ErrorCode.EC_NO_ERROR,
                 UserType.USER_SETTINGS, upstreamEvents,
                 currentTimeMillis() - wifiTetheringStartTime);