Ovulation and Fertile Window Calculator

Ovulation is estimated by counting back a luteal phase of about 14 days from your next period. With a 28-day cycle that puts ovulation on day 14, so the date is the first day of your last period plus your cycle length minus 14. A longer cycle moves ovulation later.

It is the span of days when intercourse can lead to pregnancy. Sperm can survive up to about five days and the egg lives roughly a day, so the window runs from five days before ovulation to one day after it. The days just before ovulation are the most fertile.

The luteal phase after ovulation stays fairly fixed at about 14 days, but the time before ovulation varies. So a longer cycle usually means you ovulate later and a shorter cycle means earlier. Entering your real average cycle length makes the estimate more accurate.

It is an estimate based on a regular cycle and an average luteal phase. Real ovulation can shift from month to month, especially if your cycles are irregular. Tracking basal body temperature or using ovulation tests gives a more precise read on your fertile days.

No. This tool is for general planning only and does not diagnose fertility or replace contraception. If you are trying to conceive, having trouble, or relying on timing to avoid pregnancy, speak with your doctor.

Yes. The calculation runs entirely in your browser. The dates you enter are never uploaded or stored.