Due date calculator

How many weeks pregnant am I?

Our due date calculator will help you work out when your baby is likely to arrive, so you can start planning ahead.

Most babies arrive within a week of their due date.

Calculate your baby's due date

Ovulation and conception usually occur about two weeks after the first day of your period, and the average pregnancy lasts between 37 and 42 weeks.

Using this information, along with the average length of your menstrual cycle, we’re able to calculate your estimated due date using our due date calculator.

Why not give it a try?

How can you figure out your due date?

As soon as you discover that you’re pregnant, you’ll probably be eager to know when your baby is likely to arrive. After all, there’s a lot to think about, particularly if you like to be prepared.

At your first appointment following a positive pregnancy test, your midwife or GP will give you an estimated due date. But if that hasn’t yet been arranged, there are several ways you can roughly calculate your estimated due date (EDD) yourself.

Due date calculator by conception date

Whilst you might know the exact day that you had sex, knowing the exact date of conception is harder to pinpoint. That’s because sperm can live inside the body for up to five days and your egg can live for 24 hours after being released from the ovary.

This means that conception can take place several days after you’ve had unprotected sex. To get a more accurate idea of your baby’s due date by conception, you’ll need to know exactly when you ovulated, as well as the exact date you had sex.

Due date based on ovulation date

Once an egg has been released from your ovaries, it has a 12 to 24 hour window in which it can be fertilised. You can check our ovulation calculator here  to help you work out when you’re going to be most fertile.

If you’ve been planning your pregnancy, you may have been tracking your ovulation, and you may be able to use this as the date of conception. If you know exactly what day you ovulated, add 266 days to this date and you’ll have an estimated pregnancy due date.

Calculate your due date based on your last period

Calculating your due date based on the first day of your last menstrual period (LMP) can work well if you have a relatively regular menstrual cycle. This won’t be as effective if you have irregular periods.

To calculate your due date based on your last period, you’ll need to know the exact date of your LMP, and also have an idea of whereabouts in your menstrual cycle you ovulate. On average, this is roughly 14 days before the start of your next cycle.

Another way to do this is to count 208 days from the first day of your LMP, which will give you an estimated due date based on a 40 week pregnancy.

IVF due date calculator

If your pregnancy journey is started with IVF (in vitro fertilisation), you can calculate your estimated due date by adding 266 days to the date that you had your embryo transfer, affording for a little more precision. 

However, your calculated due date may vary slightly depending on which day you had the embryo transfer after fertilisation.

For example:

• For a 3 day blastocyst this would be your transfer date + 266 days (or 38 weeks) minus 3 days.
• For a 5 day blastocyst this would be your transfer date + 266 days (or 38 weeks) minus 5 days.

Will my due date change when I have a scan?

You’ll get a more accurate due date once you have your dating scan.  This usually happens at around week 12 of your pregnancy and is the most accurate way to find out exactly how many weeks pregnant you are.

It is possible to have earlier or later scans, but if you do so earlier than 7 weeks and later than 14, the measurements of your baby won’t be as precise when it comes to calculating your due date.

You can learn more about pregnancy scans here.

How accurate are due dates?

However, you calculate your due date, it will only ever be an estimate. Only 4% of babies actually arrive on their due date, with approximately 90% of babies arriving in the two weeks before or after.

Ultimately, due dates give you a good idea of when you can expect your baby to be born, rather than a definitive date.