Habit Streak Calculator
Your consistency rate, how a streak compares to it, and how long a habit takes to reach a target at your actual completion rate.
Consistency is completions over days available.
How the habit streak calculator works
Consistency is completions over days available. The useful insight is that a long streak and a high consistency rate are different things: someone at 95% consistency will break streaks constantly, and someone at 70% can have one long run and a lot of empty weeks.
The research figure of "66 days to form a habit" is a median with an enormous range — 18 to 254 days in the original study. This projects your own rate rather than repeating the number.
Formula: consistency = completions / days; days to target = target / rate
Worked examples
| Inputs | Consistency | Note |
|---|---|---|
| 68 of 90 days | 75.56% | 75.6% consistency |
| Near-perfect | 97.78% | much longer expected runs |
| Struggling | 33.33% | runs of under a day on average |
FAQFrequently asked questions
How long does it take to form a habit?
The often-quoted 66 days is a median. The study behind it found a range from 18 to 254 days, so a single number is not much use.
Is a streak or a rate more useful?
The rate. A streak is one sample of it, and streak-chasing makes a single missed day feel like failure when the rate barely moved.
Why is the expected streak so short?
Because runs are fragile. At 75% consistency the average unbroken run is three days, even though three quarters of days are completed.
What consistency should I aim for?
Eighty per cent is genuinely good for most habits. Perfection is neither necessary nor sustainable.
Does missing a day reset progress?
No — it moves the rate by one day out of however many. That is the argument for tracking the rate rather than the streak.
Where these figures come from
- ISO 8601 — Date and time — Representations for information interchange — the yyyy-mm-dd format and the week-numbering rules used here
- US Naval Observatory — Calendars — the Gregorian leap-year rule
- GOV.UK — bank holidays — bank holidays by nation (not applied here)
Last checked: September 2026. The Gregorian calendar rules do not change; working-day counts exclude Saturdays and Sundays only.