Know your baseline
Add consecutive period start dates to find the average, shortest, and longest cycle in your recent sample—without uploading any health data.
Your dates stay on this device. Nothing you enter here is saved or sent to Flowy.
The calculation
Cycle length is the number of days from the first day of one period to the day before the next period starts. Enter consecutive period starts and we calculate each interval.
The displayed average is rounded to the nearest whole day. The shortest, longest, and individual intervals stay visible so the average never hides the underlying dates.
Good to know
An average smooths out differences. Always look at the shortest and longest recent cycles too; two people can have the same average with very different patterns.
Cycle timing can change with age, stress, illness, contraception, pregnancy, breastfeeding, perimenopause, and health conditions. A calculator describes dates—it does not diagnose their cause.
Common questions
Count from the first day of one period up to—but not including—the first day of the next. This calculator finds that interval for each pair of dates and averages the results.
Two period dates produce one cycle length, but several recent cycles give a more useful picture. Keep tracking if you have only a small sample or your timing changes.
The Office on Women’s Health describes a normal cycle as 24 to 38 days, while emphasizing that cycles differ and can change with age and life circumstances.
Not necessarily. A short list of dates cannot diagnose an irregular cycle. Look at the pattern over time and seek medical advice if timing changes concern you or comes with other symptoms.
