Why streaks work — and where they break

The "21 days to form a habit" line you've heard a hundred times is a misquote of Maxwell Maltz's 1960 self-help book. A real 2009 study by Phillippa Lally et al. (UCL) found the median time to automaticity was 66 days, with a range from 18 to 254. Some habits are quick (drink a glass of water); others take months (a 20-minute run).

What consistently works is the cue → routine → reward loop popularised by Charles Duhigg in The Power of Habit. A visible tracker makes the routine itself the reward — checking the box becomes a tiny, immediate dopamine hit that smooths over the days when the underlying habit is harder.

What this tracker does

• Up to a dozen habits, each a single editable row.
• Last 21 days visible at once. Today is on the right. Tap any cell to mark a day done; tap again to clear.
• Honest streak counter. Shows your current consecutive-day streak. Today not yet done doesn't break the streak — you have until midnight.
• 30-day completion rate so you can see real consistency (e.g. "73%") rather than just chasing the streak number.
• No account, no sync, no telemetry. Data lives in your browser. The tradeoff: clearing browser data loses your history.

How to actually build a habit with this

1. Pick fewer habits than you think. Two new habits at once is hard; four is a setup for failure. Add one. Lock it in for a month. Then add the next.
2. Make the habit small enough that you can never reasonably say no. "Read 1 page" beats "read 30 minutes." "5 push-ups" beats "go to the gym."
3. Stack the new habit onto an existing one. After I pour my morning coffee, I do 5 push-ups. Existing routines provide the cue.
4. Don't miss twice. A single missed day is just a missed day. Two in a row is the start of a broken habit. Re-engage the next morning, no guilt narrative.
5. Review the 30-day percentage, not just the streak. A 14-day streak with 50% lifetime consistency is fragile; an 8-day streak with 90% consistency is durable.

What this tracker won't do

• It won't nag you with push notifications. Reminders for a specific time of day are a job for the Reminders tool or a system alarm.
• It won't follow you across devices unless you upgrade to Pro and sign in.
• It won't share your streak with a friend. Habit accountability via a partner is well-evidenced but lives in a different tool.