Ovulation Calculator

If you're trying to conceive, timing matters. This ovulation calculator uses the first day of your last period and your usual cycle length to estimate your fertile window, your most likelyovulation day and when your next periods are due — for the next six cycles, shown on a calendar. It runs entirely in your browser; nothing you enter is stored or sent anywhere.

How to use it

Enter the first day of your last period.
Set your average cycle length (from the first day of one period to the first day of the next).
Plan around the highlighted fertile days, especially the two days before ovulation.

Example

If your last period started on 1 October and your cycle is 28 days, your next period is due on 29 October. Ovulation is likely around 15 October, so your fertile window is roughly 10–16 October, with the best chances on 13–15 October. A home pregnancy test is most reliable from the day your period is due. Once pregnant, find your due date with thepregnancy due date calculator, or keep a record with theperiod tracker.

Health disclaimer: This tool gives general estimates for information only and is not medical advice, diagnosis or treatment. Please consult a qualified doctor about your health. Read the full disclaimer.

Frequently asked questions

How is the ovulation date calculated?

Ovulation usually happens about 14 days before the next period starts. So with a 28-day cycle it is around day 14, and with a 32-day cycle around day 18 (counting the first day of your period as day 1).

What is the fertile window?

The 6 days ending on the day after ovulation — the 5 days before ovulation plus ovulation day. Sperm can survive up to about 5 days, while the egg lives about 12–24 hours, so these are the days when pregnancy is most likely.

How accurate is an ovulation calculator?

It is a good guide for regular cycles, but ovulation can shift with stress, illness, travel or conditions like PCOS. Ovulation test kits, basal body temperature or cervical mucus changes give more personal confirmation. A doctor can track ovulation with ultrasound.

Can I use this to avoid pregnancy?

Calendar methods alone are not reliable contraception, especially if cycles vary. Speak to a doctor or gynaecologist about effective family-planning options.

Is my data saved?

No. Everything is calculated in your browser and nothing is sent anywhere. To keep a record of your periods on this device, use the period tracker.