When am I most fertile?

You're most fertile in the two to three days leading up to and including ovulation — the peak of the roughly six-day fertile window.

Is this calculator accurate if my cycles are irregular?

The calendar method is least reliable with irregular cycles because ovulation timing changes. An ovulation predictor kit or symptom tracking gives a better estimate.

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Ovulation Calculator — Find Your Fertile Window

Estimate your ovulation day and most fertile days from your cycle.

First day of your last period Average cycle length (days)

A typical cycle is 28 days; anywhere from 21 to 35 is common.

Enter your last period date to see your estimate.

Estimate only — not medical advice. This calculator uses the standard calendar method and assumes regular cycles. Ovulation timing varies between people and cycles. It is not a form of contraception and should not be relied on to prevent or achieve pregnancy. Consult a healthcare professional for personal advice.

How does the ovulation calculator work?

De ovulation calculator estimates when you're likely to ovulate based on your cycle. Ovulation usually happens about 14 days before your next period starts, regardless of how long your cycle is. From the first day of your last period and your average cycle length, the tool works out your expected ovulation day and your fertile window — the roughly six days (five days before ovulation plus the day itself) when conception is most likely, because sperm can survive several days and the egg lives about 24 hours.

What is the fertile window?

The fertile window is the span of days in your cycle when intercourse can lead to pregnancy. It ends on ovulation day and begins about five days earlier. Outside this window the chance of conception is very low. Because ovulation can shift from cycle to cycle, ovulation predictor kits and tracking symptoms (like basal body temperature and cervical mucus) give a more precise picture than the calendar alone.

Frequently asked questions

You're most fertile in the two to three days leading up to and including ovulation. That's the peak of the roughly six-day fertile window this calculator highlights.

The calendar method is least reliable with irregular cycles, because ovulation timing changes. If your cycle length varies a lot, an ovulation predictor kit or tracking your symptoms will give a better estimate.

No. This is an estimate, not a contraceptive method. Because ovulation can occur earlier or later than predicted, it must not be relied on to avoid pregnancy. Use a proven contraceptive method and speak to a healthcare professional.

Yes. The calculation happens entirely in your browser. Your dates are never uploaded, stored or shared.

Quick facts

✓ Ovulation day estimate
✓ 6-day fertile window
✓ Next period prediction
✓ Estimated due date
✓ 100% private