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Ovulation calculator and fertility calendar

This tool can help you learn about your menstrual cycle and determine your most fertile days of the month.

Our ovulation calculator and fertility calendar show you when you're most fertile, to help improve your chances of getting pregnant. Every woman's menstrual cycle is unique, so discovering your own fertile window will help you work out when you have the best chance of conceiving a baby.

What is the fertile window?

Your fertile window is the best time of the month to try for a baby, based on your menstrual cycle. It includes the five days leading up to ovulation, and the day of ovulation itself.

Ovulation is when your ovaries release an egg for sperm to fertilise. It usually happens about two weeks before your period starts.

Sperm can live in your body for a few days, so you may conceive if you have sex in the days leading up to ovulation. During the 24 hours after ovulation, the egg travels down the fallopian tube towards your womb; if the egg meets a sperm at this point, conception could also happen then.

How does the ovulation calculator work?

To find out your fertile window and increase your chances of getting pregnant, just put in the first day of your last period and how long your cycle usually lasts (between 20 and 45 days).

Our calculator will work out when your cycle will end, and count back two weeks to estimate when you may ovulate. It will then create a personalised fertility calendar showing your full fertile window each month for the next six months.

The ovulation calculator shows you all your upcoming fertile days, and when your baby will be due if you do conceive. So you'll have all the information you need to start planning your pregnancy.

NOTE: This tool provides approximate dates only and assumes a regular menstrual cycle. The timing of your fertile window can be unpredictable, even if your cycles are usually regular.

What if I have an irregular menstrual cycle?

If your cycles are irregular, you may have trouble pinpointing your day of ovulation based on this calendar alone. Find out about ovulation predictor kits (OPKs), or read more ways to predict ovulation using your basal body temperature, cervical mucus and more.

What is ovulation?

Ovulation is when your ovaries release an egg each month, usually about two weeks before your period starts.

Once an egg has been released, it's ready to be fertilised. When you have sex, sperm can live inside your body, waiting for an egg to be released, for up to a week. So having sex in the days before ovulation, and on the day you ovulate, gives you the best chance of getting pregnant.

After ovulation, your egg travels down the fallopian tube towards your womb. It can stay alive for 12-24 hours after ovulation, so there's also a chance of getting pregnant the day after ovulation, too.

The main hormones involved in ovulation are luteinising hormone (LH) and follicle stimulating hormone (FSH). At the right point in your cycle, the brain produces these hormones, which prompt the ovaries to release an egg.

On an average 28-day cycle, ovulation most often happens 14 days after the first day of your period. The time between the first day of your period and ovulation is known as the follicular phase, while the time after ovulation is known as the luteal phase.

However, the exact dates of these phases can vary from woman to woman, and even cycle to cycle. There are several factors that can influence when you ovulate, including stress and using certain medications.

Learn more about ovulation and how your menstrual cycle works.

How else can I tell my most fertile days?

Our calculator will estimate the dates up to, and including the day of ovulation, which is when you're most fertile. But there are other signs and symptoms of ovulation that can give you a clue to your fertile window. These include:

Basal body temperature

Your basal body temperature (BBT) is your temperature first thing in the morning. Many women see a spike in their temperature shortly after ovulation, which can be a sign that you've ovulated.

Because this increase in temperature happens after ovulation, it won't help you conceive during this cycle. However, by tracking your temperature over time, you may learn when you can expect to ovulate next and use this to work out your next fertile window.

Learn more about charting your BBT.

Cervical mucus

Cervical mucus (CM) is the natural vaginal discharge that most women produce. The colour and texture can change throughout the month.

Around the time of ovulation, your cervical mucus may be clear and slippery, a bit like raw egg white. This is likely to happen during your most fertile days, so it's a good time to have sex if you want to conceive.

See what fertile cervical mucus looks like.

Changes to your cervix

Throughout the month, your cervix changes in position and texture. This can also give you some indication of when you ovulate.

Around the time of ovulation, the cervix is often said to be short, high, open and wet (SHOW). Find out what this means and how to check it in our expert guide to checking your cervix for ovulation.

More ways to predict ovulation

Ovulation tests

The most common type of ovulation test works a lot like a pregnancy test. It detects the level of luteinising hormone (LH) in your pee. LH is the hormone that triggers ovulation, so a positive result means you're likely to ovulate soon, making it the perfect time to have sex if you want to get pregnant.

Ovulation tests can be particularly helpful if you have an irregular cycle, when it may be hard to track symptoms like basal body temperature and cervical mucus. You'll usually need to test for several days to pick up an increase in LH, but the instructions with the kit will tell you what to do.

There are other types of test that help to indicate ovulation by measuring changes in your saliva, though these are less common.

Learn more about ovulation tests and how to use them.

Fertility tracking apps

There are lots of different apps available to help track your menstrual cycle and work out when ovulation is most likely. These rely on regularly tracking your periods, plus other symptoms such as your temperature and changes to your cervical mucus.

Fertility apps can be helpful in working out when you ovulate, but you do have to track your symptoms every day for the best results. See what fertility tracking apps other women recommend in the BabyCentre community.

Should I only have sex when I'm most fertile?

Planning sex for your fertile window may be helpful if you find it difficult to have regular sex, for example, if you or your partner often work away. But for many couples, timing and charts can be stressful and take the spontaneity out of sex.

In general, simply having sex every two to three days throughout your cycle will give you the best chance of conceiving. That way, no matter when you ovulate, there will be sperm ready and waiting to fertilise your egg as it's released.

Give yourselves the best chances of getting pregnant with our nine tips for quick conception.

Can conceiving at certain times increase my chances of having a boy or a girl?

No. There is a theory – known as the Shettles method – which suggests that:

  • having sex during or after the day of ovulation is more likely to conceive a boy
  • having sex from the end of your period to three days before ovulation is more likely to conceive a girl

However, there is no evidence to support this theory.

Can conceiving at certain times increase my chances of having twins?

No, unfortunately there's no surefire way to increase the chances of having twins. It may be more likely to happen for you if you're having fertility treatment, are over 35, or if twins run in your family.

Learn more about the chances of having twins.

BabyCentre's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. When creating and updating content, we rely on credible sources: respected health organisations, professional groups of doctors and other experts, and published studies in peer-reviewed journals. We believe you should always know the source of the information you're seeing. Learn more about our editorial and medical review policies.

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Bastian LA, Brown HL. 2023. Clinical manifestations and diagnosis of early pregnancy. UpToDate. https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-early-pregnancyOpens a new window [Accessed September 2023]

Faust L et al. 2019. Findings from a mobile application-based cohort are consistent with established knowledge of the menstrual cycle, fertile window, and conception. Fertil Steril. 2019 Sep;112(3):450-457.e3. https://pubmed.ncbi.nlm.nih.gov/31272722/Opens a new window [Accessed May 2023]

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NHS. 2022a. How can I tell when I'm ovulating? NHS, Common Health Questions. https://www.nhs.uk/common-health-questions/womens-health/how-can-i-tell-when-i-am-ovulating/Opens a new window [Accessed May 2023]

NHS. 2022b. Pregnant with twins. NHS, Pregnancy. https://www.nhs.uk/pregnancy/finding-out/pregnant-with-twins/Opens a new window [Accessed May 2023]

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NHS. nd. Ovulation failure. The Shropshire and Mid Wales Fertility Centre. https://www.shropshireivf.nhs.uk/about-fertility/causes-of-infertility/failure-of-ovulation/Opens a new window [September June 2023]

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