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Ovulation Calculator

Find your fertile window and predicted ovulation date — instantly, privately, and free.

Count from the first day of one period to the first day of the next. Most cycles are 24–35 days.

How does ovulation prediction work?

Ovulation typically occurs 14 days before your next period — this is called the luteal phase, and it's remarkably consistent across women. What varies is the follicular phase (the days between your period and ovulation).

This calculator uses the standard calendar method: cycle length - 14 = ovulation day. Your fertile window spans 5 days before ovulation through 1 day after, because sperm can survive up to 5 days and the egg lives 12-24 hours.

For more accurate predictions, sign up for Bloom — our multi-signal algorithm combines BBT temperature tracking, cervical mucus patterns, OPK results, and cycle history to predict ovulation with clinical-grade accuracy.