BabyCentre's due date calculator
Have you been trying to work out your baby’s due date and found yourself adding, subtracting, multiplying and counting on your fingers? Working out your due date can be confusing, but luckily, our handy pregnancy due date calculator can help you easily find out when your baby might make an appearance.
Simply use our free calculator above to find out your estimated due date based on the first day of your last period, your conception date, ultrasound details or your IVF transfer date.
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Our advanced due date calculator won’t just show your due date – it also shows your whole pregnancy timeline, from how many weeks pregnant you are, to when your antenatal appointments may happen, and even when you can expect to feel your baby move for the first time.
How we calculate your baby’s due date
The date of your last period
Even if you've been tracking your ovulation, it's difficult to know for sure exactly when you ovulated and conceived. That's why your baby’s due date is often based on the date of your last period instead. Health professionals often call this your LMP, or last menstrual period.
Most women ovulate about two weeks after the first day of their period, and conceive shortly afterwards. However, it depends on the length of your menstrual cycle. If you usually go less than 28 days between periods, you probably ovulated and conceived a bit earlier, while if your cycle is longer, you probably conceived a bit later.
Our calculator can take the date of your last menstrual period and your typical cycle length to discover the days you were most likely to have been fertile.
The average pregnancy lasts between 37 weeks and 42 weeks. Our pregnancy due date calculator uses this information to give you an estimated due date (EDD).
Conception date
The challenge with using your conception date is that getting it right can be tricky as you won’t necessarily conceive on the day you have sex.
Sperm can live in a woman’s body for up to five days, and the ovum (egg) can live for up to 24 hours after being released. That gives you a six-day window when you might conceive. If you’re pretty sure of your conception date though, our calculator can use that to estimate when your baby may be due.
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IVF transfer date
If you conceived through IVF, our calculator can work out your due date using your IVF transfer date. If you had a day 5 embryo transfer, it will count 261 days from your transfer date. If you had a day 3 embryo transfer, it will count 263 days.
Ultrasound scan dates
Your first pregnancy scan will probably happen when you're between 10 weeks and 14 weeks pregnant. It's known as the dating scan, and is used to give you a more accurate due date, based on the size and development of your baby. If you've had a scan before then, you can put the details in our calculator to estimate your due date. Learn more about antenatal scans.
Will my baby definitely be born on my due date?
Your due date is a best guesstimate, but unfortunately, no-one can say for sure exactly when your little one will arrive. In fact, only about 4% of babies (1 in 20) are born on their exact due date!
However, it is likely that your baby will arrive in the few weeks either side of your estimated due date (EDD). Knowing this can help you to be prepared for labour and birth, and to have everything ready for your new baby.
Could my baby’s due date change?
Yes, it’s possible that a doctor might give you a different due date at one of your antenatal appointments. This can happen for a number of reasons. For example, if you have an irregular menstrual cycle, you may have ovulated and conceived a bit earlier or later than you thought. A lot of other factors can also play havoc with your cycle and make it more difficult to tell when you conceived, including stress, weight loss and weight gain.
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It’s also easy to confuse implantation bleeding with a regular period, in which case, your due date could be wrong by as much as a month.
If your doctor gives you a different due date at your pregnancy scan, their suggested date is more likely to be accurate. But even then, there’s no telling for sure exactly what day your baby will appear!
How long can you go over your due date?
Most people go into labour naturally by 42 weeks (two weeks after your due date). If you’re still pregnant at 39 to 41 weeks, you’ll be offered a membrane sweep. If that doesn’t work, you’ll be offered induced labour. It’s not recommended to go more than 2 weeks after your due date because the risk of stillbirth increases after 42 weeks.
When can I take a pregnancy test?
If you’re trying for a baby you’ll probably be keen to take a pregnancy test as soon as possible. Try to be patient, you’ll get a more reliable result if you wait a few days after your missed period, or two weeks after your IVF transfer date, before taking a test.
Home pregnancy tests detect the presence of the pregnancy hormone, called human chorionic gonadotrophin (hCG), in your wee. If you test too early there may not be enough hCG in your body for a home pregnancy test to show an accurate reading.
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Levels of hCG are typically fairly high at around six to seven weeks of pregnancy (that is, six to seven weeks after the first day of your last period). By then you should get a definite result. You might even be showing signs of pregnancy!
Check out our week by week information from the start of your pregnancy:
