Period Calculator
Predict your next several period dates from your last period and cycle length.
Assumptions used in this calculation
- Regular cycles: Assumes your cycle length stays consistent; actual cycles can vary month to month.
About this calculator
Manually counting forward several cycle lengths on a calendar to predict upcoming periods gets tedious and error-prone past the first one or two months, especially when planning travel or events around your cycle. This calculator takes the first day of your last period and your average cycle length, then projects forward to list several upcoming expected period start dates at once (each future date equals your last period plus cycle length multiplied by the number of cycles ahead), instead of making you re-add the cycle length by hand each time. It's useful for anyone who wants a quick look-ahead view rather than tracking day by day in an app. Because the projection assumes your cycle length stays constant, predictions naturally get less reliable further into the future, stress, illness, travel, and normal biological variation can all shift actual cycle length from month to month, so treat later predicted dates as increasingly approximate rather than fixed.
Worked example
Last period Jan 1, 2026, 28-day cycle, 3 cycles ahead
Result: Next periods: Jan 29, Feb 26, Mar 26
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