Ovulation calculator: When will I ovulate?

Our easy-to-use ovulation calculator will help work out when you're most fertile.

Hand holding a test to illustrate ovulation calculator
(Image credit: Getty images / Future)

An ovulation calculator can help to identify when you are most fertile and the few days of the month that are your best chance of getting pregnant. 

Using an ovulation calculator is a great way to manage your fertility and predict when ovulation might happen and it also helps take away some of the confusion around tracking cycles naturally - especially if your periods aren't regular. Anything to help your fertile egg get together with strong sperm.

Menstrual cycles are all different, they can range from 22 days right up to 36 days. Though an “average menstrual cycle” begins on the first day of your period and continues right up to the day before you start the next one, about 28 days on average. If you're trying to conceive, knowing your ovulation date is essential.

"Some people find it reassuring to monitor signs of ovulation and feel confident they are taking control over their fertility." Dr Matthew Prior, fertility consultant and medical director at Dr Fertility says.

For our ovulation calculator you need to know your average menstrual cycle and when your luteal phase begins. The luteal phase is the second half of your menstrual cycle. This starts after ovulation and ends with the first day of your period.

Your luteal phase usually lasts 12 to 16 days, with an average of 14 days for most women, so if you’re unsure we’d recommend choosing 14 days on the calculator.

What is an ovulation calculator and how does it help you get pregnant?

An ovulation calculator helps you to estimate how likely you are to ovulate on certain days in your cycle so you can identify your most fertile days, the ones that are prime for conception. These calculators work by taking the first day of your last period and the length of that menstrual cycle to give a range of days when you may release an egg.

"Some people find it reassuring to monitor signs of ovulation and feel confident they are taking control over boosting their fertility." Dr Matthew Prior says. He goes on to add, "However, some research shows that getting too hung up on your cycle can cause more stress and take away the enjoyment of trying to conceive causing unnecessary pressure. If this is the case it may be a good idea to stop monitoring for a few months." 

How to use our free ovulation calculator

Our ovulation calculator helps you identify when you're ovulating, i.e. releasing an egg, on a certain day of your menstrual cycle. It could help you to further identify your most fertile days and so help with conception.

Work out your ovulation date using our tool below:

Ovulation Calculator

Use our calculator to find out when you'll ovulate and when your due date is.

As with most ovulation tools, be aware that the dates given are an estimate and as Mr Raef Faris from the Lister Fertility Clinic, says, they can’t guarantee the ovulation date will be 100 per cent accurate. 

If you conceive outside of your ovulation dates for example, this will impact your due date. If you have any doubts, it's best to contact your GP, especially as there are a whole number of factors from age to conditions like endometriosis that can affect fertility.

Downloading and using calendar apps on your phone are also a way to track period dates and cycle lengths, to predict when you might ovulate. Though, Fertility Nurse Kate Davies from Dr Fertility says a calendar app could be misleading. "[ovulation] is usually estimated to be around the middle of your cycle. However, it is well documented in the research that even having a regular 28-day cycle doesn’t mean you will always ovulate on day 14.

"Therefore, using and relying solely on a calendar App can actually be misleading. I encourage women to consider observing their natural fertility indicators (temperature and cervical mucus) and using this information to become empowered and knowledgeable on their cycle, fertility, and ovulation."

Doctors, such as Mr Raef Faris from the Lister Fertility Clinic, also warn that "[fertility calculators] are not very accurate and may result in missing the appropriate window for conception."

However, if you're struggling to conceive and looking to identify potentially your most fertile period, then it is worth trying a calculator like this, to see if you conceive.

What is an ovulation calendar and how do you use one?

An ovulation calendar is a tool used to help identify your most fertile days, it can also help you to track your menstrual cycle. After working out the ovulation date using the calculator, many couples turn to an ovulation calendar - sometimes known as a fertility calendar - to figure out the days of the month where they're most likely to conceive if they have sex.

It works as sperm can live in the body for up to five days after sex, so conception can occur even if you've had sex four or five days before ovulation begins. The fertility window is normally around six days, as that is the amount of days that the egg and sperm can survive. To figure out this fertile period, plot your menstrual cycle on a calendar then count back 14 days from the expected last day of your next cycle. This will be your most fertile day.

Alternatively, there are a number of apps that will do this for you - such as Clue.

When will I ovulate? How to work out your ovulation date

Ovulation happens about 14 days before your period starts, also called menstruation. ‘Normal’ menstruation differs from person to person. Bleeding from three to seven days is considered the norm. While it may feel short, three days of bleeding is still considered normal as long as you're menstruating regularly. And each full menstrual cycle can last anywhere from 21 to 35 days. 

For example, if your average menstrual cycle is 28 days, you ovulate around day 14, and your most fertile days are days 12, 13 and 14. If your average menstrual cycle is 35 days then ovulation happens around day 21 and your most fertile days are days 19, 20 and 21. 

image of a 28 day cycle to illustrate ovulation calculator

(Image credit: Getty / Future)

Though studies in the British Medical Journal show that in only about 30% [of people] is the fertile window entirely within days 11-13. And that most  people reach their fertile window earlier and others much later. This means that the timing of their fertile window can be highly unpredictable, even if their cycles are usually regular.

And, while using the ovulation calculator above can help you to work out your ovulation date, there are other ways to work out when you might be ovulating to, according to our experts.

"There are a few methods used mostly depending on the hormone surge that occurs prior ovulation." Mr Faris says, "This includes temperature rise, cervical mucus and urine ovulation."

He warns, however, "They may not be accurate as some women may not show signs of ovulation but would have ovulated already. The best advice would be trying naturally (every 2-3 days) soon after the period is over till day 20 of the cycle, but it could be extended (depending on the length of the cycle)."

While Dr Matthew Prior explains, "Some women can tell if they are ovulating where others can’t. When you ovulate, you may notice a change in your discharge and a slight increase in temperature or change in urine ovulation predictor kits.

"While these are all useful tools there is no evidence to suggest monitoring your cycles improves your chance of getting pregnant. This is because sperm can survive for several days in the reproductive system so as long as you are having sex every couple of days it is not important to get the timing to coincide with ovulation." 

But if you want to try it, here's a step-by-step guide to working out your ovulation date...

"While these are all useful tools there is no evidence to suggest monitoring your cycles improve your chance of getting pregnant. This is because sperm can survive for several days in the reproductive system so as long as you are having sex every couple of days it is not important to get the timing to coincide with ovulation." 

But if you want to try it, here's a step by step guide to working out your ovulation date...

Step 1: Your menstrual cycle

When your next period starts, make a note of the date. The following month, when your period comes again, make a note of this date, then count the days in between. This will give you your cycle length. You may need to do this for more than one month and take the average, especially if your cycle isn't regular. Remember also that coming off the Pill will reveal your true menstrual cycle.


Period starts = 1st January Next period starts = 3rd February

Days in between (including 1st Jan but not 3rd Feb) = 33 days.

This means your menstrual cycle length is 33.

Step 2: Your fertile dates

Using our ovulation calendar, find the right number in the menstrual cycle length column (33 for the above example) and read across for your ovulation day and most fertile days.

Swipe to scroll horizontally
22Day 8Days 7-9
23Day 9Days 8-10
24Day 10Days 9-11
25Day 11Days 10-12
26Day 12Days 11-13
27Day 13Days 12-14
28Day 14Days 13-15
29Day 15Days 14-16
30Day 16Days 15-17
31Day 17Days 16-18
32Day 18Days 17-19
33Day 19Days 18-20
34Day 20Days 19-21
35Day 21Days 20-22
36Day 22Days 21-23

Step 3: Your ovulation date

Work out your ovulation and most fertile dates. For the below example:

First day of last period = 3rd February 2021

Cycle Length = 33

Ovulation (19 days later) = 22nd February 2021

Most fertile (18-20 days later) = 21st and 23rd February 2021

Once you know your ovulation date, as a rule, you are most fertile the day before, during and the day after.

N.B. These figures are based on averages and should be used as a guide only. Days and dates may differ from person to person.

I have irregular periods, when will I ovulate?

No matter the length of her period, every woman ovulates about 14 days before her next period. So, if you have a 28-day cycle, you'll ovulate on day 14, and if you have a 32-day cycle, you'll ovulate on day 18.

Mr Faris advises that the ovulation date in this case could vary, so "it would be useful to try regularly after the period and not to rely on the ovulation kits." This is because, as Dr Matthew Prior says, "Having regular periods is the best sign of ovulation. In fact, fertility specialists may not even advise bloods to check if ovulation has happened because regular cycles are a sure sign of ovulation."

How to track your fertility

The best way to track fertility is through your natural fertility indicators, fertility nurse Kate Davies says, which includes checking your own temperature and cervical mucus.

"These fertility indicators, used together, can give you a reliable indication of when you are in your fertile time. You can choose to use systems to help you interpret your physiological data such as Apps and fertility monitors and some women also choose to use ovulation predictor kits to help identify when ovulation is about to occur." 

Clearblue Digital Ovulation Test Kit

Blue and purple packaging

(Image credit: Clearblue)

Make use of this at-home urine test to work out the two days of the month that you are most fertile, making it that little bit easier to conceive. This test is easy to use and easy to read, making the whole process as simple as possible.

Clearblue Ovulation Test - Connected

Blue and purple packaging with baby on the front

(Image credit: Clearblue)

According to Clearblue, this test is "clinically proven to double your chances of getting pregnant in the first cycle of use, versus not using ovulation tests". This ovulation test is connected to phone, to make it that much easier to track your most fertile days with the click of a button.

One Step 100x Ovulation Strips

Green and white packaging

(Image credit: One Step)

Another way to track your most fertile days, simply test these strips in a urine sample, leave it in there for 5-10 seconds, and read the results according to the instructions that come in the pack - it couldn't be simpler.

Conceive Plus Fertility Lubricant + Magnesium and Calcium

Pink and white packaging

(Image credit: Conceive Plus)

This fertility lubricant claims to help support sperm viability in order to help you to conceive, and help make the process easier for you and your partner.

Seven Seas Trying For A Baby - 28 pack

Purple packaging with seven seas red logo

(Image credit: Seven Seas)

This pre-conception supplement contains folic acid, which is often recommended to women who are looking to fall pregnant. It's also advised for some women to continue taking folic acid into the first 12 weeks of pregnancy, but it's important to consult your doctor on taking supplements during your pregnancy.

Wellman Vitabiotics Conception 30 Tablets

Dark blue with silver logo packaging

(Image credit: Wellman)

These tablets provide a combination of vitamins, minerals and bio-active nutrients to help with conception and spermatogenesis - the production of male sperm. It also includes zinc, which is said to be an important mineral for the male reproductive system.

SpermCheck Fertility Home Sperm Test Kit

Light blue and dark blue packaging with couple onfront

(Image credit: Spermcheck Fertility)

This easy-to-use at-home test kit can help to determine the concentration of sperm in your partner, and can help you find out within minutes whether his sperm count is within the normal range. However, it is advised that you seek medical advice if you are having trouble conceiving as they will be able to offer more comprehensive results on sperm count.