Safe Period Calculator

Estimate the fertile window from your last period and average cycle length.

First day of last period

The first day of your most recent menstrual period.

Average cycle length

days

Calendar estimates are approximate and depend on a regular cycle. This is NOT a reliable contraceptive method. For reference only — not medical advice.

Estimate

Enter a period date to see the estimate.

How to use

1Enter the first day of your last period and your average cycle length.
2Read the estimated fertile window and the days before and after it.
3For reference only — do not rely on it to prevent pregnancy.

Examples

28-day cycle: The fertile window is estimated around mid-cycle.