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Ovulation calculator - determine your most fertile days

Knowing the signs of ovulation and using a fertility calendar can help you to work out the best time to get pregnant. Once you can spot the symptoms and know your cycle, you'll be able to identify the time when you're at your most fertile. This means that when you're trying to get pregnant, you can concentrate your baby-making efforts on the days when the odds are in your favour.

By Mumsnet HQ | Last updated Jul 15, 2021

Date circled in red on a calendar

In association with

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First Response Rapid Result pregnancy tests provide easy-to-read results in just 45 seconds on the day of your missed period. Want to know sooner than that? Try the First Response Early Result test which allows you to take a test as early as six days before the day of your missed period.


How do you know when you are most fertile?

Use our quick and easy calculator tool below to find out the days each month that you are at your most fertile. Simply enter the date your last period started and the menstrual cycle length (this is the number of days from the start of one period to the day before the next one). The calendar below will then highlight the dates when you're most likely to conceive.

Ovulation Calculator

You're at your most fertile during the days leading up to ovulation, and on the day itself. To maximise your chances of conceiving, use our calculator to work out your most fertile dates.

Enter the date your last period started

How long is your menstrual cycle?


When am I ovulating?

Contrary to what some biology textbooks may tell you, most women do not ovulate like clockwork 14 days before their period. Menstrual cycles can last between 24 and 35 days, and ovulation can happen anywhere between 10 and 16 days before menstruation begins.

Do you have irregular periods (your average cycle length varies from month to month, or is consistently shorter than 24 days or longer than 35 days)? In that case, it might be a bit trickier to work out when you are most fertile – but it's not impossible. There are various reasons for irregular cycles – including things like stress, certain medications and being underweight, so it's a good idea to visit your GP to discuss this when you start trying for a baby.

What are the symptoms?

Look out for signs such as changes in your body temperature, cervix and cervical mucus, and how you feel in general. Nearer to the event, your cervical mucus will take on a stickier quality, a bit like egg whites, and will look whiter than usual. You might find you get sore breasts, too, and experience slight lower abdominal pain on one side. Keeping track of any changes throughout the month by recording your basal body temperature can help you recognise your own symptoms. You'll also understand the length of your cycle better, and at which point you're most likely to get pregnant.

Ovulation predictor kits

If you find the physical signs hard to spot, you might also want to try an ovulation test. Predictor kits (or OPKs) make it easier to zero in on your fertile window and do away with some of the head-scratching – especially if you're not sure how long your cycle is. There are two types of tests available – one that measures the level of luteinising hormone (LH) in your urine, and one that measures the amount of salt in your saliva. If you opt for the wee test, you're looking for a surge in LH, which means you're a couple of days away from releasing an egg and in prime baby-making time. It's best to take the test around lunchtime, rather than first thing in the morning. Try not to drink too much water in the hours before, as this could dilute your urine and make it hard to detect the LH.

If you choose the saliva-based tests, you'll need to use a small microscope and some slides to check the salt in your saliva (lab coat optional). You'll need to lick the slide and then let it dry. If it dries clear, you've not reached your fertile window. If it dries with a little patch of salt residue that looks a bit like a fern leaf, you're entering the most fertile time in your cycle. However, saliva tests don't necessarily work perfectly for all women, and can be disrupted by external factors such as eating, drinking and smoking. So it's best to use it in conjunction with the calculator.

Best time to get pregnant

It's recommended that, if you’re trying to get pregnant, you should be having sex throughout your cycle in order to increase your chances – every other day is the optimum. However, the best time to conceive is in the two days before ovulation (usually days 12 to 14) in preparation for the egg being released. If you use lubricant, you may want to consider switching to a sperm-friendly option while you're trying to get pregnant.

Before you start, find out how you can prepare your body and mind for conception throughout the month, to improve your chances of getting pregnant in your fertile time. There are also important lifestyle changes your partner may need to take into account in order to keep his sperm count as high as possible. After 28 days of tracking, testing and Doing the Deed, it's time to grab a pregnancy test and keep your fingers crossed for a BFP (Big Fat Positive).


What First Response has to say

“Getting pregnant can take time and require several testing moments. We know that testing for pregnancy can be an overwhelming and stressful experience. That's why we at First Response endeavour to keep the reading of your pregnancy test results clear, and fast. Our First Response Rapid Result test provides easy-to-read results in just 45 seconds. With our First Response Early Result test pregnancy readings are ready within three minutes. The Early Result test also allows you to take the test six days earlier than your missed period.

All of our pregnancy tests are over 99% accurate at detecting typical pregnancy hormone levels. All you need to do is decide whether you want to find out whether you are pregnant on the day of your missed period (Rapid Result) or up to six days before your missed period (Early Result)."

Find out more about First Response