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Ovulation calculator

Enter the first day of your last period and how long your cycle is. You see the estimated ovulation, your fertile days and your next period.

It is an estimate for regular cycles. It is not a method of contraception and not a substitute for advice from a health professional.

How it's calculated

Ovulation usually happens 14 days before the next period: first day of your last period + cycle length − 14.
The fertile window runs from 5 days before ovulation to the day after, because sperm can live up to 5 days.
Your next period is due one cycle after the last one.

An example

With a last period on March 5, 2026 and a 28-day cycle, estimated ovulation is March 19, 2026.

The fertile window runs from March 14, 2026 to March 20, 2026, and the next period is due on April 2, 2026.

Frequently asked questions

Which are the most fertile days?

The two or three days before ovulation and the day of ovulation. The whole window lasts about 6 days.

Does it work if my cycle is irregular?

It gives you an idea, but a less precise one. With irregular cycles, ovulation can move by several days from month to month.

Can I use this to avoid pregnancy?

No. The estimate is approximate and ovulation can come early or late. To prevent pregnancy, use a method of contraception.

Key terms

Ovulation: When an ovary releases an egg.
Fertile window: The days in the cycle when pregnancy is possible.

The same calculation in other countries

Up-to-date official data

We check the official sources automatically, every day.

See all sources

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