Cycle Length Calculator
Your cycle length is the number of days from the first day of one period to the first day of the next. This calculator works it out from two recent period start dates.
Once you know your average, every other prediction — periods, ovulation, phases — becomes far more accurate.
Sync your whole cycle, automatically
PhaseBloom builds your meals, workouts, and skincare around your exact cycle phase, day by day.
How it works
Enter the first day of a recent period and the first day of the period before it. We count the days between them.
For a more reliable average, repeat this over a few cycles. Most cycles fall between 21 and 35 days.
Frequently asked questions
Is a 26-day or 32-day cycle normal?
Yes. Anything from 21 to 35 days is considered normal. Consistency matters more than hitting exactly 28.
Why does my cycle length change?
Stress, travel, sleep, illness, and big training or diet changes can all shift a cycle by a few days. Occasional variation is normal.