diff --git a/includes/utilities.php b/includes/utilities.php
index 788307b..5ea4211 100644
--- a/includes/utilities.php
+++ b/includes/utilities.php
@@ -283,3 +283,52 @@ function consoleLog( $data ) {
     echo 'console.log(' . json_encode($data) . ')';
     echo '</script>';
 }
+
+/**
+ * Backfill the running_balance column for any user rows that have NULL.
+ *
+ * The v2 API's `data.balance` field is the vault balance after each entry.
+ * If the column is missing for a row, treating it as NULL means
+ * MAX(running_balance) ignores it. This routine fetches the latest entry's
+ * balance from the API and broadcasts it to all NULL rows of the user,
+ * so the displayed balance becomes accurate after the first sync following
+ * the schema upgrade.
+ *
+ * @param PDO    $pdo  Database connection.
+ * @param string $user The user whose NULL rows should be backfilled.
+ *
+ * @return void
+ */
+function backfillRunningBalances($pdo, $user) {
+    if (!array_key_exists($user, USER_KEYS)) {
+        throw new ApiKeyMissingException("User does not have an API key configured.");
+    }
+
+    $countStmt = $pdo->prepare('SELECT COUNT(*) FROM vault WHERE user = :user AND running_balance IS NULL');
+    $countStmt->bindValue(':user', $user);
+    $countStmt->execute();
+
+    if ((int)$countStmt->fetchColumn() === 0) {
+        return;
+    }
+
+    $url = 'https://api.torn.com/v2/user?selections=log&log=5850,5851&limit=1&sort=DESC';
+    $responseData = executeApiCall($url, USER_KEYS[$user]);
+    validateApiResponse($responseData);
+
+    if (empty($responseData['log'])) {
+        return;
+    }
+
+    $latest = $responseData['log'][0];
+    if (!isset($latest['data']['balance'])) {
+        return;
+    }
+
+    $balance = (int)$latest['data']['balance'];
+
+    $updateStmt = $pdo->prepare('UPDATE vault SET running_balance = :balance WHERE user = :user AND running_balance IS NULL');
+    $updateStmt->bindValue(':balance', $balance);
+    $updateStmt->bindValue(':user', $user);
+    $updateStmt->execute();
+}