Period Calculator
Estimate your next period and fertile window from your last period date and cycle length.
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Estimated next period
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How to use the Period Calculator
- Enter the date your last period started.
- Enter your average cycle length (default 28 days).
- Read your estimated next period date and fertile window.
Frequently asked questions
How is the fertile window estimated?
Ovulation is estimated around 14 days before your next expected period, which is the basis for the fertile window shown here. Actual timing varies by individual.