3weeks
Build habits in 21 days — the science-backed habit tracker
iOS
About
Just 21 days can change your life.
Do you set goals every new year only to give up within a week? The problem isn't willpower — it's the lack of a proper system. Science shows it takes a minimum of 21 consecutive days to wire a new behavior into your brain as a habit. Three weeks. Every single day. After that, the action is no longer an "effort" — it's just part of your day.
3weeks is a habit-formation planner built on this principle.
Features
- 21-Day Challenge System — Start the countdown the moment you add a habit; one tap to check in each day
- Streak Tracking — Watching your streak grow makes quitting feel impossible
- Daily Log — Record your mood and completion score; attach photos or videos
- Badge Rewards — Earn badges at 7 days, 21 days, 60 days, and 90 days
- Statistics — Calendar view, weekly check-in patterns, mood graph, and average completion rate
- 5 Languages — Korean, English, Japanese, Chinese, and German
- Cloud Sync — Sign in with Google or Apple ID; your records follow you across devices