○Free calculator

Ovulation calculator

Trying to conceive? Estimate your ovulation day, your fertile window and when your next period is due – for this cycle and the next three.

Average cycle length
Next cycles
Fertile daysOvulationPeriod starts
Estimated ovulation
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Fertile window
Next period
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How to use the ovulation calculator

  1. Enter the first day of your last period.
  2. Set your average cycle length – the number of days from the first day of one period to the first day of the next.
  3. You will see your estimated ovulation date, your fertile window, your next period and the next three cycles.

How it works

The second half of the cycle (the luteal phase) is fairly constant at about 14 days, so ovulation usually happens around 14 days before the next period – not necessarily on day 14.

Ovulation ≈ first day of last period + cycle length − 14

Sperm can survive for up to five days and an egg for about 12–24 hours, so the fertile window is the five days before ovulation, the day of ovulation and the day after.

Worked example

If your last period started on 1 November 2026 and your cycle is 28 days long, ovulation is expected around 15 November, your fertile window is 10–16 November and your next period is due on 29 November. With a 32-day cycle, ovulation moves to about 19 November.

Signs of ovulation

  • Cervical mucus becomes clear, slippery and stretchy, like raw egg white.
  • Basal body temperature rises by about 0.2–0.5 °C after ovulation.
  • Ovulation tests detect the LH surge 24–36 hours before ovulation.

Cycles vary from month to month, so these dates are estimates. This calculator must not be used as contraception. If you have irregular cycles or have been trying to conceive for a year (six months if you are over 35), talk to a doctor.

Frequently asked questions

When am I most fertile?
The two to three days before ovulation and the day of ovulation itself give the highest chance of pregnancy.
Can I ovulate with an irregular cycle?
Yes, but it is harder to predict. Ovulation tests, temperature charting or a doctor’s advice are more reliable than a calendar calculation.
When can I take a pregnancy test?
Most home tests are reliable from the day your period is due. Testing earlier may give a false negative.

Last reviewed: November 13, 2026

Results are estimates for general information only and are not financial, tax, medical or legal advice. Check important figures with a qualified professional.