diff --git a/scripts/backfill-streaks.js b/scripts/backfill-streaks.js
new file mode 100644
index 00000000..8456441a
--- /dev/null
+++ b/scripts/backfill-streaks.js
@@ -0,0 +1,85 @@
+"use strict";
+
+const fs = require("fs").promises;
+const fsSync = require("fs");
+const path = require("path");
+
+async function calculateStreaks(history) {
+  if (!history || history.length === 0) {
+    return { currentStreak: 0, longestStreak: 0, lastUpdated: null };
+  }
+
+  const sortedHistory = [...history].sort(
+    (a, b) => new Date(a.date) - new Date(b.date),
+  );
+
+  let currentStreak = 0;
+  let longestStreak = 0;
+  let lastActiveDate = null;
+  let previousTotal = -1;
+
+  for (const entry of sortedHistory) {
+    const currentTotal =
+      (entry.easy || 0) + (entry.medium || 0) + (entry.hard || 0);
+    const entryDate = new Date(entry.date);
+
+    if (currentTotal > previousTotal) {
+      if (!lastActiveDate) {
+        currentStreak = 1;
+      } else {
+        const diffDays = Math.round(
+          (entryDate - lastActiveDate) / (1000 * 60 * 60 * 24),
+        );
+
+        if (diffDays === 1) {
+          currentStreak++;
+        } else if (diffDays > 1) {
+          currentStreak = 1;
+        }
+      }
+
+      longestStreak = Math.max(longestStreak, currentStreak);
+      lastActiveDate = entryDate;
+    }
+
+    previousTotal = currentTotal;
+  }
+
+  return {
+    currentStreak,
+    longestStreak,
+    lastUpdated: lastActiveDate
+      ? lastActiveDate.toISOString().split("T")[0]
+      : null,
+  };
+}
+
+async function runBackfill() {
+  const DATA_DIR = process.env.DATA_DIR || path.join(__dirname, "..", "data");
+  const userDataDir = path.join(DATA_DIR, "user-data");
+
+  try {
+    const files = await fs.readdir(userDataDir);
+    const jsonFiles = files.filter((f) => f.endsWith(".json"));
+
+    for (const file of jsonFiles) {
+      const filePath = path.join(userDataDir, file);
+      const userData = JSON.parse(await fs.readFile(filePath, "utf8"));
+
+      const streaks = await calculateStreaks(userData.history);
+
+      userData.streak = {
+        current: streaks.currentStreak,
+        longest: streaks.longestStreak,
+        lastUpdated: streaks.lastUpdated,
+      };
+
+      await fs.writeFile(filePath, JSON.stringify(userData, null, 2));
+    }
+  } catch (err) {
+    console.error(`Backfill failed: ${err.message}`);
+    process.exit(1);
+  }
+}
+
+runBackfill();
diff --git a/scripts/sync-leaderboard.js b/scripts/sync-leaderboard.js
index 0d85d551..1309a165 100644
--- a/scripts/sync-leaderboard.js
+++ b/scripts/sync-leaderboard.js
@@ -95,6 +95,47 @@ async function updateUserDataAsync(user, DATA_DIR, ranksObj = null) {
   if (ranksObj) {
     userData.leaderboardRanks = ranksObj;
   }
+
+  const today = new Date().toISOString().split("T")[0];
+  const yesterday = new Date();
+  yesterday.setDate(yesterday.getDate() - 1);
+  const yesterdayStr = yesterday.toISOString().split("T")[0];
+
+  if (!userData.streak) {
+    userData.streak = { current: 0, longest: 0, lastUpdated: null };
+  }
+
+  const totalSolvedToday =
+    (user.data.easySolved || 0) +
+    (user.data.mediumSolved || 0) +
+    (user.data.hardSolved || 0);
+
+  const totalSolvedYesterday =
+    history.length > 1
+      ? history[history.length - 2].easy +
+        history[history.length - 2].medium +
+        history[history.length - 2].hard
+      : 0;
+
+  if (
+    userData.streak.lastUpdated &&
+    userData.streak.lastUpdated < yesterdayStr
+  ) {
+    userData.streak.current = 0;
+  }
+
+  if (
+    totalSolvedToday > totalSolvedYesterday &&
+    userData.streak.lastUpdated !== today
+  ) {
+    userData.streak.current += 1;
+    userData.streak.lastUpdated = today;
+
+    if (userData.streak.current > (userData.streak.longest || 0)) {
+      userData.streak.longest = userData.streak.current;
+    }
+  }
+
   await atomicWrite(userDataPath, userData);
 }