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Ovulation Calculator

Estimate when you're likely to ovulate and your most fertile days, based on the first day of your last period and your average cycle length. Useful whether you're trying to conceive or simply tracking your cycle.

Your cycle

Estimates assume a luteal phase of about 14 days. Actual ovulation varies — use alongside other signs if tracking closely.

Estimated ovulation
Jun 10, 2026

  • Most fertile days
  • Next period
  • Est. pregnancy test from
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How it works

Ovulation typically occurs about 14 days before your next period starts (the luteal phase is fairly constant). So:

Ovulation ≈ (LMP + cycle length) − 14 days

The fertile window spans roughly the 5 days before ovulation plus ovulation day, because sperm can survive several days while the egg lives about 24 hours.

Worked example

Last period started Jun 1, 28-day cycle:

Frequently asked questions

How reliable is the calendar method?
It gives a useful estimate but assumes regular cycles and a typical 14-day luteal phase. Ovulation can vary month to month, so for closer tracking combine it with signs like basal body temperature, cervical mucus, or ovulation predictor kits.
What are the most fertile days?
The two to three days leading up to and including ovulation are the most fertile. Because sperm can live up to about five days, the full fertile window is roughly the five days before ovulation plus ovulation day.
Can I use this to avoid pregnancy?
Calendar estimates alone are not a reliable form of contraception, since ovulation timing varies and the fertile window can shift. If you're avoiding pregnancy, use a proven contraceptive method and talk to a healthcare provider.

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