Ovulation Calculator

Ovulation typically happens about 14 days before your next period starts, not 14 days after your last one began — so this calculator uses the first day of your last period plus your average cycle length to work backward and estimate both the ovulation date and the several days around it considered your fertile window.

This is a statistical estimate built on a typical luteal phase length, not a measurement of what's actually happening in your body that cycle. Cycle length varies month to month for most people, stress and illness can shift ovulation earlier or later, and this calculator has no way to detect any of that — it just does the standard date math.

It's commonly used by people trying to conceive who want to time things around their most fertile days, or by anyone tracking their cycle who wants a quick estimate without switching to a dedicated app.

Fertility timing is deeply personal information, so nothing you enter here is transmitted or stored — the estimate is generated and shown to you entirely within your own browser.

Ovulation is estimated at (cycle length − 14) days after the start of your last period — the 14-day figure is the typical luteal phase (the time between ovulation and the next period), which tends to be more consistent across people than the follicular phase that precedes it.

The fertile window spans from five days before estimated ovulation through the day after, reflecting that sperm can survive several days in the reproductive tract while the egg itself is viable for roughly a day after release.