diff --git a/backend/tests/streakTracker.unit.test.js b/backend/tests/streakTracker.unit.test.js
new file mode 100644
index 00000000..fd3c795b
--- /dev/null
+++ b/backend/tests/streakTracker.unit.test.js
@@ -0,0 +1,59 @@
+import { describe, it, expect } from 'vitest';
+const { applyStreakForActivity, getUTCDayDifference, resetStreakIfMissed } = require('../utils/streakTracker');
+
+describe('streakTracker', () => {
+  describe('applyStreakForActivity', () => {
+    it('unlocks 3-Day Streak when streak reaches 3', () => {
+      const user = { currentStreak: 3, unlockedAchievements: [], lastPracticeDate: new Date() };
+      const newlyUnlocked = applyStreakForActivity(user);
+      expect(user.unlockedAchievements).toContain('3-Day Streak');
+      expect(newlyUnlocked).toContain('3-Day Streak');
+    });
+
+    it('unlocks 7-Day Streak when streak reaches 7', () => {
+      const user = { currentStreak: 7, unlockedAchievements: ['3-Day Streak'], lastPracticeDate: new Date() };
+      const newlyUnlocked = applyStreakForActivity(user);
+      expect(user.unlockedAchievements).toContain('7-Day Streak');
+      expect(newlyUnlocked).toContain('7-Day Streak');
+    });
+
+    it('unlocks 14-Day Streak when streak reaches 14', () => {
+      const user = { currentStreak: 14, unlockedAchievements: ['3-Day Streak', '7-Day Streak'], lastPracticeDate: new Date() };
+      const newlyUnlocked = applyStreakForActivity(user);
+      expect(user.unlockedAchievements).toContain('14-Day Streak');
+      expect(newlyUnlocked).toContain('14-Day Streak');
+    });
+
+    it('unlocks 30-Day Streak when streak reaches 30', () => {
+      const user = { currentStreak: 30, unlockedAchievements: ['3-Day Streak', '7-Day Streak', '14-Day Streak'], lastPracticeDate: new Date() };
+      const newlyUnlocked = applyStreakForActivity(user);
+      expect(user.unlockedAchievements).toContain('30-Day Streak');
+      expect(newlyUnlocked).toContain('30-Day Streak');
+    });
+
+    it('does not duplicate already unlocked achievements', () => {
+      const user = { currentStreak: 14, unlockedAchievements: ['3-Day Streak', '7-Day Streak', '14-Day Streak'], lastPracticeDate: new Date() };
+      const newlyUnlocked = applyStreakForActivity(user);
+      expect(newlyUnlocked).toEqual([]);
+      expect(user.unlockedAchievements.filter((a) => a === '14-Day Streak').length).toBe(1);
+    });
+  });
+
+  describe('getUTCDayDifference', () => {
+    it('calculates exact day differences in UTC', () => {
+      const d1 = new Date('2026-08-01T10:00:00Z');
+      const d2 = new Date('2026-08-02T10:00:00Z');
+      expect(getUTCDayDifference(d1, d2)).toBe(1);
+    });
+  });
+
+  describe('resetStreakIfMissed', () => {
+    it('resets streak if practice was missed for more than 1 day', () => {
+      const pastDate = new Date(Date.now() - 3 * 24 * 60 * 60 * 1000);
+      const user = { lastPracticeDate: pastDate, currentStreak: 10 };
+      const reset = resetStreakIfMissed(user);
+      expect(reset).toBe(true);
+      expect(user.currentStreak).toBe(0);
+    });
+  });
+});
diff --git a/backend/utils/streakTracker.js b/backend/utils/streakTracker.js
index e25e64e1..584d5cde 100644
--- a/backend/utils/streakTracker.js
+++ b/backend/utils/streakTracker.js
@@ -3,6 +3,7 @@ const User = require("../models/User");
 const STREAK_MILESTONES = [
   { days: 3, badge: "3-Day Streak" },
   { days: 7, badge: "7-Day Streak" },
+  { days: 14, badge: "14-Day Streak" },
   { days: 30, badge: "30-Day Streak" },
 ];