Ovulation calculator

Estimate your fertile window and likely ovulation date.

First day of last period

Average cycle length (days)

Est. ovulation date

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Fertile window starts

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Fertile window ends

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Next period est.

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Why cycles vary

Ovulation typically occurs about 14 days before the next period starts, regardless of cycle length — so a longer cycle usually means ovulation happens later, not that the luteal phase changes much. Stress, illness, and travel can all shift the actual date. Already expecting? Try the due date calculator.

This tool estimates averages and is not a reliable method of contraception or fertility diagnosis.

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