Ovulation Calculator
Enter your last period date and cycle length to see your estimated ovulation date and the 6-day fertile window when conception is most likely.
Ovulation typically occurs about 14 days before your next period — so for a 28-day cycle, that's day 14, and for a 35-day cycle, it's day 21. Your fertile window spans the 5 days before ovulation plus ovulation day itself. This calculator estimates your fertile window based on your last menstrual period date and average cycle length.
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Last reviewed: April 2026Report an error
Estimated Ovulation Date
Apr 29, 2026
Your estimated ovulation date is Apr 29, 2026. Your fertile window is Apr 24, 2026 – Apr 30, 2026. Next period expected around May 13, 2026.
Fertile Window (6 days)
Apr 24, 2026 → Apr 30, 2026
Days Until Ovulation
9 days
Next Period
May 13, 2026
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How to Use This Ovulation Calculator
- Enter the first day of your most recent period.
- Enter your average cycle length (count from day 1 of one period to day 1 of the next).
- Read your estimated ovulation date (most fertile day).
- Note the 6-day fertile window — the 5 days before ovulation plus ovulation day.
- Track 2–3 cycles to identify your personal pattern; use ovulation predictor kits (OPKs) for confirmation.
Frequently Asked Questions
- The best time is the 6-day fertile window: the 5 days leading up to ovulation plus the day of ovulation itself. Sperm can survive up to 5 days in the reproductive tract, while an egg is viable for 12–24 hours after release.
- This calculator gives an estimate based on your cycle length. For confirmation, use an ovulation predictor kit (OPK) to detect the LH surge, or track basal body temperature (BBT) — which rises ~0.2°C after ovulation.
- Irregular cycles make calendar-based prediction less reliable. Ovulation predictor kits, BBT charting, or monitoring cervical mucus are more accurate methods. Talk to your OB-GYN if cycles vary by more than 7 days regularly.
- It's very unlikely but possible, since cycle length can vary month to month. No calendar method is 100% reliable for either achieving or avoiding pregnancy.
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