Ovulation Calculator
Estimated ovulation date + fertile window from your last menstrual period. Standard cycle-based math; useful for tracking but not for contraception.
Predicted window
Ovulation
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Fertile window starts
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Fertile window ends
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Next period expected
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How the dates are calculated
Ovulation typically occurs ~14 days before the next period, regardless of cycle length. With your last period and cycle length, the calculator predicts the next period (last + cycle days) and counts back 14 days for ovulation.
The fertile window is roughly 5 days before ovulation through 1 day after — sperm can survive ~5 days in the female reproductive tract; an egg lives ~24 hours after release. Sex during this window has the highest chance of conception.
Why this isn't reliable for contraception
Cycle length varies. Ovulation timing varies. Stress, illness, and many factors shift the actual day. The calendar method has a real-world failure rate of 12–24% per year as contraception. For pregnancy prevention, use a method with much higher efficacy.
For trying to conceive
Useful as a starting point. More accurate alternatives: ovulation predictor kit tests (detect LH surge ~36 hours before ovulation), basal body temperature tracking (catches ovulation retrospectively), cervical mucus monitoring. Most people conceive within 6 months of intentional tracking.