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Habit streak calculator

See how consistent you have been, how far along you are, and when your new habit is likely to start feeling automatic.

Updated October 30, 2026. Free, nothing to sign up for, and nothing you type leaves your browser.

How the calculator works

• Planned days so far counts every day from your start date up to today, scaled by how many days a week you planned. Five days a week over four weeks is 20 planned days.
• Days done is planned days minus the days you missed. Consistency is days done divided by planned days.
• Projected date assumes you keep the same consistency from here and tells you when your days done will reach your target.
• The 1% figure is 1.01 raised to the number of days done. It is a picture of compounding, not a measurement of you.

What the research says about how long a habit takes

• The 66-day study. Phillippa Lally and colleagues at University College London followed 96 volunteers who each picked one new daily eating, drinking or exercise behavior and reported every day how automatic it felt. The median time to reach their plateau was 66 days, with a range of 18 to 254 days. (Lally et al., European Journal of Social Psychology, 2010.)
• Missing a day did not reset the clock. The same study found that missing one opportunity did not materially affect habit formation. That is why this calculator asks how many days you missed instead of treating your streak as broken.
• A 2024 review agrees. A systematic review and meta-analysis of health habit studies from the University of South Australia found median times of 59 to 66 days and a range of 4 to 335 days. Doing the behavior consistently and in the same context each day helped habits form. (Singh et al., Healthcare, 2024.)
• The 21-day myth traces back to a 1960 self-help book, Psycho-Cybernetics, where plastic surgeon Maxwell Maltz wrote that patients needed a minimum of about 21 days to adjust to a change. It was an observation about adjusting, not a study of habits.

How to keep a streak going

• Never miss twice. One missed day barely matters. Two in a row is how a habit quietly stops. James Clear, author of Atomic Habits, makes this his rule.
• Attach it to something you already do. "After I pour my coffee, I write one sentence." Doing it in the same context each day is one of the factors the 2024 review linked to habit formation.
• Shrink it on bad days. If the plan is 30 minutes of reading, a single page still counts as showing up.
• Mark it somewhere you can see. A calendar with an X for each day done turns consistency into something you can see.

For more on building habits, see the best podcasts about habits and how 1% Better compares with James Clear's 3-2-1.

Link to this calculator

Writers and teachers are welcome to link to this page. Its address will not change: https://b-e-t-t-e-r.com/tools/habit-streak-calculator/