Challenge Completion Rate Calculator
Enter days completed and days elapsed to get your real completion rate, where the current pace lands you, and how many days you can still afford to miss.
Challenge Completion Rate Calculator
Where you are now
Days completed is the number you actually logged. Days elapsed is every day since you started, including today.
Total challenge length
Target completion rate
The finishing percentage you want to hit, measured against the full challenge length.
Doing this sum by hand is the part nobody keeps up for 30 days straight. LockIn30 reads it off your log instead: one habit, a grid you tick, and a statistics screen with the rate, the streak and the misses already worked out.
See your stats automatically in LockIn30Everything is calculated in your browser. Nothing you type is sent anywhere or stored.
Days elapsed or total days: why two calculators give you different numbers
Take one log: 18 days completed, 22 days elapsed, on a 30-day challenge. Divide by days elapsed and you get 81.8%. Divide by total days and you get 60.0%. Same log, same person, two numbers that sit nearly 22 points apart. Neither is wrong, and this is the single most common reason an app and a spreadsheet disagree about the same challenge.
The elapsed denominator measures form. It answers "of the chances I have had so far, how many did I take", and it moves every day. The total denominator measures outcome. It answers "how much of the whole challenge is in the bank", and because the bottom number is fixed at 30 it always looks low early on, even if you have not missed a single day. On day 3 of a perfect run, the total-based rate is 10%.
They converge on the last day, when days elapsed equals total days and both formulas spit out the same result. Until then, use the elapsed rate on yourself mid-challenge. It is the honest read on how you are doing right now. Judge the finished challenge by the total-days rate instead, since that is the outcome you actually walked away with. LockIn30's in-app statistics use the elapsed convention, and so does the headline number above.
What counts as a good completion rate
The working band is 70 to 80%. High enough that the behaviour starts to feel automatic, loose enough to survive a stomach bug or a week where work eats everything. Most habit coaches treat 80% held across two consecutive weeks as the marker that something has turned into a routine rather than a project you are managing.
Lally et al. (2010) found that a single missed opportunity did not derail habit formation: automaticity gains picked back up afterwards. The practical version of that is the never-miss-twice rule. One miss is noise. Two in a row is where a slip becomes a pattern, and the odds of quitting climb sharply on that second day.
Which is the argument against the 100%-or-restart instinct. Finishing 26 of 30 days is 86.7%, a genuinely good outcome, and the person who restarts from day 1 after one miss usually ends up with fewer completed days than the person who shrugged and logged day 5 anyway. Chasing perfection is how most challenges end early.
One caveat on percentages: distribution matters as much as the number. 70% built from one miss every three days is a habit under construction. The same 70% built from a nine-day gap in the middle is two short challenges with a hole between them.
Your miss budget at every challenge length
Your budget is the total challenge length minus the days it takes to hit your target. Worked out for the lengths people actually run:
| Length | 70% target | 80% target | 90% target | 100% target |
|---|---|---|---|---|
| 30 days | 21 done, 9 misses | 24 done, 6 misses | 27 done, 3 misses | 30 done, 0 misses |
| 60 days | 42 done, 18 misses | 48 done, 12 misses | 54 done, 6 misses | 60 done, 0 misses |
| 66 days | 47 done, 19 misses | 53 done, 13 misses | 60 done, 6 misses | 66 done, 0 misses |
| 75 days | 53 done, 22 misses | 60 done, 15 misses | 68 done, 7 misses | 75 done, 0 misses |
| 90 days | 63 done, 27 misses | 72 done, 18 misses | 81 done, 9 misses | 90 done, 0 misses |
Partial days always round up. 90% of 75 days is 67.5, which becomes 68, because logging three quarters of a day is not a thing. Same reason 70% of 66 days (46.2) becomes 47.
The useful shift is treating that budget as something you spend deliberately. Knowing you have 6 misses on a 30-day run at 80% turns a bad Tuesday into a planned withdrawal instead of a failure. It also tells you when the account is empty, which is the number the calculator above keeps in front of you as it shrinks.
What a missed day costs you in strict vs forgiving mode
In forgiving mode a miss lands in the denominator and you keep going. Your rate drops a few points, the day shows as incomplete on the grid, and the challenge carries on from where it was. That is the mode the maths on this page assumes.
In strict mode a missed day surfaces the Be Honest dialog the next time you open the dashboard, and you pick one: acknowledge the misses and continue, or restart from day 1. A restart zeroes both counters, so the new attempt begins at 100% with the full miss budget back.
This is also where a 100% target dies. After a single miss on a 30-day run, the best rate still possible is 96.7%, so 100% is arithmetically gone for that attempt no matter what you do next. Forcing that decision is the whole point of strict mode, and it is why the calculator flags an unreachable target rather than quietly showing you a zero.
LockIn30 works all of this out from your log: completion rate, current and best streak, days missed, and how much of the challenge is left. You pick the habit and tick the day. The percentages take care of themselves.
Frequently Asked Questions
Common questions about challenge completion rate calculator
What is a good habit completion rate?
80% is the number most habit coaches point at, and holding it two weeks running is the usual sign a behaviour has stopped being a project. In practice anything in the 70 to 80% band works: high enough for the thing to start feeling automatic, slack enough to absorb a sick day. On a 30-day challenge that is 24 days for 80% and 27 for 90%. You do not need perfect. You need most days.
Should I divide by days elapsed or total challenge days?
Both, depending on what you are asking. While the challenge is running, divide by days elapsed: that is your current form, and it moves every day (18 of 22 elapsed is 81.8%). Once it is over, or when you want to know where you would land, divide by total days. That denominator never changes, so early on it looks dreadful even when you have missed nothing (18 of 30 is 60.0%). The headline above uses elapsed days, the projection uses total days, which is why the two disagree. Same reason your app and your spreadsheet can report very different percentages for one log.
Is 70% consistency enough to build a habit?
For habit formation, yes. Lally et al. (2010) at UCL found that missing a single opportunity to perform the behaviour did not derail the process, and automaticity kept climbing afterwards. The percentage matters less than the shape of the misses. 70% as one miss every three days builds a habit. The same 70% as one solid nine-day gap usually does not.
Does missing one day break my streak or my habit?
It breaks the streak, not the habit. The logic behind "never miss twice" is that one missed rep gets absorbed, while two in a row is where the abandonment risk jumps, because the second miss is what turns a slip into a new pattern. Miss one day of 30 and you still finish at 96.7%. If you would rather have a day grid do the counting, the 30-day habit challenge tracker logs each day for you.
How many days can I miss in a 30-day challenge and still hit 80%?
Six. 80% of 30 is 24 days, so 30 minus 24 leaves 6. Other lengths at the same target: 12 misses on a 60-day run, 15 on a 75-day run, 18 on a 90-day run. Push the target to 90% and those drop to 3, 6, 7 and 9. The "days you can still miss" output above runs the same sum against where you actually are rather than the whole challenge, so it shrinks as you spend it.
How do I calculate completion rate for a 75-day challenge?
Same formula, different denominator: days completed divided by days elapsed, times 100, for as long as the challenge is running. Finishing a 75-day run at 80% takes 60 completed days, which leaves you 15 misses to play with. At 90% it is 68 days, because 67.5 rounds up and you cannot log three quarters of a day. To work out the date your 75 days actually run out, use the 30-day challenge end date calculator.
What does "projected final rate at this pace" actually mean?
It is where you finish if the rest of the challenge goes the way the first part went. One quirk worth knowing: at a perfectly held pace the projected final rate is mathematically identical to your current rate, because the arithmetic cancels out. This calculator projects in whole days instead, which nudges the number a little and gives you something concrete like "you would finish with 25 of 30 days". Either way, the forecast only moves when your behaviour does.
Does a missed day count differently in strict mode?
It does in LockIn30. In forgiving mode a miss is just a miss: the day is logged as incomplete, your rate drops a bit, and you carry on. In strict mode a missed day triggers the Be Honest flow the next time you open the dashboard, and you either acknowledge the misses or restart from day 1. A restart resets the numerator and the denominator together, so the new attempt starts at 100% again.