Ovulation and Fertile Window Calculator

Estimate ovulation, the fertile window and your next period from cycle length, with six cycles and clear assumptions. Local calculation; unsuitable for contraception.

Cycle detailsThe estimate depends on cycle regularity and average length.

First day of last period

Average cycle length

days

As-of date

All dates are Gregorian. Calculations run in your browser without sending your data.

An informational estimateCycles and ovulation can vary from month to month. Do not use these results for contraception or diagnosis.

Health reference ↗

ACOG ↗

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