How long does ovulation last? Your fertile window explained

Ovulation itself is quick: an ovary releases an egg, and that egg can only be fertilised for up to about a day. But because sperm can survive inside you for several days, the time when sex can lead to a pregnancy, your fertile window, is about 6 days long.

How long does ovulation last?

The release of the egg happens once a cycle, usually 10 to 16 days before your next period. The egg can only be fertilised for up to about a day after it’s released, so your most fertile days are the few days before you ovulate and the day itself.

Sperm last much longer. They can survive in the fallopian tubes for up to 7 days after sex. So sperm from sex a few days before you ovulate can already be waiting when the egg is released.

What is the fertile window?

It’s the days in each cycle when sex can lead to a pregnancy. A well-known study that tracked couples trying for a baby found pregnancies only happened from sex in the 6 days ending on the day of ovulation. The chance was lowest 5 days before ovulation, at about 1 in 10, and highest on the day of ovulation itself, at about 1 in 3.

In other words, the best days are the few days before you ovulate and the day itself, not the days after.

When is my fertile window?

In a regular 28-day cycle, ovulation is likely to be around day 14, counting the first day of your period as day 1. That puts the fertile window at roughly days 9 to 14. But only about 13% of cycles are actually 28 days long, and ovulation often doesn’t happen on day 14. In a study of more than 600,000 cycles tracked with an app, the average cycle was 29.3 days.

To work out your own window, start from when your next period is due and count back:

Ovulation: usually 10 to 16 days before your next period.
Fertile window: the 5 days before ovulation, plus the day of ovulation.

For example, with a 32-day cycle you might ovulate somewhere around day 16 to 22, so your fertile window could start as early as day 11. Because it’s hard to pin down the exact day, having sex every 2 to 3 days through your cycle means you don’t need to.

If your cycle is irregular

If your cycle length changes a lot from month to month, it’s much harder to predict ovulation from dates alone. Watching for changes in your discharge, or using ovulation tests, can help. Our guide to tracking ovulation compares the options. If your periods are very irregular or have stopped, see your GP.

Can you get pregnant outside the fertile window?

No, but your fertile window can move without you realising. It’s possible, though not very likely, to get pregnant soon after a period finishes if you ovulate early or have a short cycle. So if you’re not trying for a baby, there’s no day of the month that’s completely safe without contraception.

How often should we have sex?

NICE, which advises the NHS, says sex every 2 to 3 days gives the best chance of pregnancy. That way there are usually sperm waiting whenever you ovulate, and you don’t have to time things exactly, which many couples find stressful. See how to improve your chances of getting pregnant for more.

Questions people ask

How many days after your period are you fertile?

It depends on your cycle length. In a 28-day cycle, the fertile window is roughly days 9 to 14, counting from the first day of your period. In shorter cycles it can start soon after your period ends.

Can you get pregnant the day after ovulation?

It’s much less likely. The egg can only be fertilised for up to about a day after it’s released, and the study above found pregnancies came from sex in the 6 days up to and including ovulation day.

Do you ovulate on the same day every month?

Not always. Ovulation can shift from cycle to cycle, even if your periods are fairly regular, which is why counting days alone isn’t very accurate.

How long after ovulation can I test?

About 2 weeks, around when your period is due. How early can I take a pregnancy test? explains early testing.

Some early tests can be used from 5 days before your period is due (the packet may say ‘6 days before your missed period’), but they won’t pick up every pregnancy that early. Testing from the day your period is due is more reliable, though a negative can still be wrong if there isn’t enough hCG yet. If your period doesn’t come, test again a few days later.

How long does ovulation last? Your fertile window explained