Period Calculator
Estimate your next period
Quick guide
What can Period Calculator help you do?
Free period calculator. Estimate your next period date and expected period range from last period date, cycle length, and period length.
Best for
Turn a previous period start, fixed cycle length, and period duration into one projected date range for planning notes. The calculator moves forward exactly one cycle. It does not create a multi-month calendar, learn from historical variation, or send a reminder on the predicted date.
How to use it
Enter the first day of the last period, cycle length, and period length. Defaults are 2026-05-10, 28 days, and 5 days. Both lengths must be positive, with period length no greater than cycle length. Use whole days; Use sample restores fixed examples, not personal records.
How to read the result
The next start is the previous start plus one cycle. The end adds period length minus one, so a five-day period includes both endpoints across five days. The calculation does not advance repeatedly to the future; an old start date can produce a range already in the past.
Privacy and limits
This component projects dates in the browser, without a built-in period diary, reminder service, or cloud synchronization. Copy result writes to your local clipboard. Site analytics and potential advertising connections still exist, so be careful about private cycle information in shared screens or pasted results.
This fixed-cycle range does not assess menstrual irregularity, pregnancy, or another health condition. Lengths must be positive whole days; invalid dates or results outside the supported years produce errors. Personal history and cycle variation are not modeled, so agreement or disagreement with the dates does not establish a medical conclusion.
Frequently Asked Questions
Can it track irregular cycles?
It estimates from the cycle length you enter. Irregular cycles may vary.
Is my data saved?
No. The calculation runs in the browser.