Cycle tracking

Ovulation Calculator

Estimate your ovulation day, fertile window and next expected period from the first day of your last period and your average cycle length.

—Estimated ovulation day
—Fertile window
—Next expected period
CyclePredicted period startPredicted ovulation
Educational estimate only, based on average cycle statistics. Actual ovulation timing varies and this is not a substitute for medical advice or a method of contraception.

Calculated on your device. Nothing is uploaded or stored on a server.

How to use the ovulation calculator

Select the first day of your most recent period, then enter your typical cycle length (from the first day of one period to the first day of the next) and your luteal phase length if you know it (14 days is a common average). The calculator estimates your ovulation date and fertile window.

How ovulation timing is estimated

Ovulation is estimated to occur a fixed number of days — your luteal phase length — before your next expected period, since the luteal phase (after ovulation) tends to be more consistent than the follicular phase (before it). The fertile window includes the five days before ovulation and the day of ovulation itself, since sperm can survive for several days while an egg survives roughly 12–24 hours.

Cycles vary naturally

Even people with regular cycles can ovulate a few days earlier or later than predicted due to stress, illness, travel or other factors.

Track over several cycles

Predictions become more accurate the more you know about your own average cycle and luteal phase length, ideally tracked over 3–6 months.

Ovulation calculator FAQ

Common questions, answered.

How is ovulation day calculated?

Ovulation is estimated as your cycle length minus your luteal phase length, counted from the first day of your last period. For a 28-day cycle with a 14-day luteal phase, that's day 14.

What is the fertile window?

It's the several days when pregnancy is possible: the five days leading up to ovulation plus the day of ovulation itself, reflecting how long sperm can survive in the body.

Why do you ask for luteal phase length separately from cycle length?

The luteal phase (from ovulation to the next period) is usually more consistent than the phase before ovulation, so using it gives a more personalized ovulation estimate than assuming a fixed mid-cycle day.

Is this accurate enough to use for contraception?

No. This is an educational estimate based on averages and should not be used as a method of contraception or to guarantee conception timing. Speak with a healthcare provider for medical guidance.

Explore more free tools: Menstrual Cycle TrackerPregnancy Due Date Calculator