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 based on the first day of your last period. And we suggest other calculation methods to use, including a due date calculation for IVF pregnancies
How we calculate your baby’s due date
Even if you've been tracking your ovulation, there's no way to know for sure exactly when you ovulated and conceived. That's why your baby’s due date is often calculated 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. 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.
Other ways to calculate your due date
Conception date
If you’ve been using an ovulation predictor kit or tracking your cycle using an app then you may be able to calculate your due date using your conception date. The challenge with this method is that getting your date of conception right can be tricky as you won’t necessarily conceive on the day you have sex.
IVF transfer date
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, then add 38 weeks to your date of conception to work out when your baby may be due.
If you conceived through IVF, you can calculate your due date using your IVF transfer date. If you had a day 5 embryo transfer, count 261 days from your transfer date. If you had a day 3 embryo transfer, count 263 days.
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 four in 100 babies are born on their due date! But it's likely that your baby will arrive in the few weeks either side of your estimated due date. Knowing this can help you to be prepared for labour and birth, and to have everything ready for your new baby.
Will my due date change when I have a scan?
It may do. 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. Learn more about antenatal scans.
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 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 , particularly before you've missed a period, there may not be enough hCG in your body for a home pregnancy test to show an accurate reading. Levels of hCG are typically fairly high at around six to seven weeks of pregnancy. So, by the time your period is a week or two weeks late, you should get a definite result. You might even be showing signs of pregnancy!
