Ovulation Calculator
Enter your last period and cycle length to estimate your ovulation day and 6-day fertile window — for this cycle and the next three.
Your dates
Your result
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Estimated ovulation day
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detail
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context
Your 40-week timeline
Heartbeat ~8w
Anatomy scan ~20w
Full term 39w
You
1st trimester2nd trimester3rd trimester
Week 1Week 13Week 27Due · 40
Based on Naegele's rule (ACOG methodology). Estimates only — always confirm with your provider.
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How ovulation timing works
Ovulation usually happens about 14 days before your next period starts — not 14 days after the last one. That's why cycle length matters: in a 32-day cycle, ovulation lands near day 18, not day 14. The egg lives only about 24 hours, but sperm can survive up to 5 days, which creates a roughly 6-day fertile window ending the day after ovulation.