Ovulation and the Fertile Window, Explained

If you are trying to conceive — or simply want to understand your cycle better — knowing when you ovulate is the single most useful thing. Conception is only possible during a short window each month, and this guide explains when that window is and how to estimate it.

What ovulation is

Ovulation is the release of a mature egg from the ovary. Once released, the egg survives for only about 12 to 24 hours. In a typical cycle, ovulation happens roughly 14 days before your next period starts — not 14 days after your last one. That distinction matters, because it means the timing depends on your cycle length.

Why the fertile window is about six days, not one

Even though the egg only lives for a day, sperm can survive inside the body for up to five days. So the “fertile window” is the five days leading up to ovulation plus the day of ovulation itself — about six days in total. The two days just before ovulation are usually the most fertile.

How to estimate your fertile days

The estimate is based on two things: the first day of your last period and your average cycle length. From those, you can work out the likely ovulation date (about 14 days before the next expected period) and then count back five days to find the start of your fertile window. Because cycles vary, this is an estimate rather than a guarantee — but it gets you to the right few days.

Body signs that confirm ovulation

• Cervical mucus becomes clear, slippery, and stretchy — similar to raw egg white — around your most fertile days.
• Basal body temperature (your temperature at rest) rises slightly just after ovulation.
• Ovulation predictor kits detect the surge in luteinising hormone (LH) that happens a day or so before ovulation.

An important note

Fertility awareness is helpful for planning a pregnancy, but it is not a reliable method of contraception on its own, because cycles are irregular for many people and sperm can survive several days. If you are avoiding pregnancy, use a proper contraceptive method.

To find your likely fertile window for this cycle, use our Ovulation Calculator — enter the first day of your last period and your cycle length to see your estimated ovulation date and most fertile days.