How is ovulation estimated?

About 14 days before your next period. The fertile window includes the 5 days before ovulation (sperm lifespan).

Can I use this for contraception?

No — it is an estimate only and not a contraceptive method.

Ovulation Calculator

Estimate your ovulation day and fertile window from your cycle. Also shows next period and due date. Free ovulation calculator.

First day of your last period

Cycle length: 28 days

21 d28 d (average)35 d

ℹ️ The calculator estimates ovulation and the fertile window from your cycle length (ovulation about 14 days before the next period). It is an estimate and should not be used for contraception.

The Ovulation Calculator estimates when ovulation, the release of an egg, happens and which days make up your fertile window, based on your menstrual cycle. It helps you see when the chance of conceiving is at its highest.

How the calculator works and what it’s for▾

How the calculator works

The calculator estimates the timing of ovulation from the length of your cycle and the start date of your last period. Around that point it maps a fertile window when conception is most likely.

Because the estimate relies on cycle regularity, the steadier your cycle, the more accurately the timing can be predicted.

What you enter and what you get

You enter the start date of your last period and your typical cycle length. The calculator shows the estimated ovulation day and the fertile window around it.

The result helps you time intercourse for the days when the chance of pregnancy is greatest.

Who it is for

The calculator serves those hoping to conceive who want to time attempts to their fertile window. It can also be used simply to track and understand your own cycle.

It is especially suited to cases where the cycle is fairly regular and its length is known.