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Calculator

Estimate your fertile window.

Enter cycle details to estimate ovulation, fertile window, peak fertility days, next period, and a suggested pregnancy test date. This calculator runs in the browser and only saves your inputs if you choose to save a cycle on this device or to your account.

Cycle details

Use averages from your recent cycles where possible.

Private

Checking save mode

Account creation is optional. Guest saves stay in this browser; account saves use your signed-in Supabase history.

Choose the first day your last period started. This should be a past or current date.

Available range: 25 Jun 2024 to 25 Jun 2026.

Cycle regularity

Results will appear here.

After calculation, you will see ovulation timing, fertile window, peak fertility days, suggested intercourse timing, next period, pregnancy test timing, confidence level, warnings, and a visual cycle calendar.