Ovulation calculator: predict your most fertile days

‘When am I ovulating?’ This is the question you might be asking if you’re trying to get pregnant. If that’s the case, it really helps to get to know your menstrual cycle, so that you can track your most fertile days. 

And our handy ovulation calculator is here to help in just a few easy steps.

Our easy-to-use ovulation or fertility calculator helps you work out your most fertile days - those days when you’re most likely to conceive. 

To get the most accurate results from the ovulation calculator, you’ll need to know:

• When your last period started
• The average length of your menstrual cycle

If you’re not sure, you can use your best guess, just bear in mind that the results won’t be as accurate.

You’re more fertile at some points of the month than others, which is good to know if you’re hoping to get pregnant. Your most fertile days are around the time you ovulate¹.

Ovulation happens when an egg is released from one of your ovaries. If it’s met and fertilised by a sperm cell as it travels down your fallopian tube to your uterus, it can develop into an embryo and result in you becoming pregnant^2,3. If the egg isn’t fertilised, it’s reabsorbed by your body and you’ll get your period.

Ovulation tends to happen between 10 and 16 days before the start of your period. If your menstrual cycle usually lasts 28 days, you’re most likely to ovulate around day 14².

It’s very tricky to pinpoint the exact moment when ovulation happens, but you can get close by using our ovulation calculator above or some of the other ovulation tracker methods listed below.

The most fertile days of your cycle are the ones that happen around ovulation. Sperm can survive in your fallopian tubes for up to 7 days after sex, making the week or so before you ovulate your most fertile².

If you’re wondering to yourself, ‘when am I ovulating?’, there are a few different ways you can get a good idea.

Your body temperature changes during ovulation, which gives you a useful way of predicting when you’re at your most fertile. 

Usually, your body temperature rises slightly when you ovulate and remains the same until you start your next period. Try taking your temperature with a digital thermometer every morning before you get out of bed. You might start to notice a pattern after a couple of cycles that helps you work out when you usually ovulate⁴.

You might notice that your vaginal discharge changes throughout your menstrual cycle. Often, it will be clear or white, thick and sticky⁵. But around four days before ovulation, it will become slippery, wet and stretchy – a little like egg whites. Once you notice that change, you’ll know you’re probably in your fertile window⁴.

You can buy tests called ovulation predictor kits (OPKs) that test your urine for hormones to tell you whether you’re ovulating (a little like a pregnancy test but to track your fertility). They can be expensive, though, so they’re not the best option for everyone⁴.

As well as changes in your body temperature and cervical mucus, you might notice other (secondary) symptoms that happen around ovulation.

These include⁶:

• Light bleeding or spotting
• Pain or cramp on one side of your pelvis (sometimes called ovulation pain or mettelschmertz)⁷
• Feeling bloated
• Sore or tender breasts
• Heightened senses of taste, vision and smell

And, most helpfully, an increased sex drive!

You can keep a diary of your symptoms throughout your menstrual cycle, or log them in a fertility tracker, to help you see patterns and work out the symptoms that usually happen around the time you ovulate.

Reviewed by Sammy, a registered NHS midwife with a background in neonatal nursing, dedicated to providing compassionate, evidence based care to women and families throughout pregnancy, birth and the postnatal period.

You’re most likely to get pregnant if you have sex around the time you ovulate. But because ovulation can be so tricky to pinpoint, the general advice is to have sex every 2 to 3 days all the way through your cycle⁴.

To get pregnant, a sperm cell needs to meet your egg while it’s still in your fallopian tube. Since sperm can survive in your body for several days after sex, the days before you ovulate are when you’re most likely to conceive⁸.

You can ovulate at any time of day. An egg is released between 10 and 12 hours after a spike in a hormone called LH⁹, which usually happens between midnight and 8am¹⁰. So the average woman can ovulate anywhere between 10am and 8pm. 

Try not to worry about the exact time you ovulate. You’re most fertile in the days around ovulation, so it doesn’t have to be an exact science. And having sex every 2 to 3 days of your cycle can give you the best chance of conceiving⁴.

Around the time you ovulate, you might notice an increase in your basal body temperature, a slippery, stretchy vaginal discharge (or cervical mucus) and other symptoms like ovulation pain or tender breasts^4,6.

If your egg hasn’t been fertilised, you’ll get a period around 2 weeks after ovulation. If your egg has been fertilised by a sperm cell, you won’t get your period, which is often the first tell-tale sign that you’re expecting².

Hyperovulation is when your ovaries release more than one egg during ovulation. When this happens, there’s a chance that more than one egg will be fertilised, and you could become pregnant with multiple babies, like twins or triplets².

There’s no evidence that hyperovulation feels any different to releasing just one egg. So you might not know unless you become pregnant and see more than one baby on your first ultrasound scan!

You’re more likely hyperovulate and become pregnant with twins if ¹¹:

• Twins run in your mum’s side of the family.
• You’ve had fertility treatment.
• You’re over 35.