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Pregnancy due date calculator

Want to know when your baby is due? Use our pregnancy calculator to work out how many weeks pregnant you are and the due date to mark in your calendar.

By Mumsnet HQ | Last updated Jun 30, 2022

Woman writing on a calendar

Calculate your baby's due date

By now you've probably done a pregnancy test (or ten) and started noticing the early signs of pregnancy – but how do you know how far along you are?

Using the first day of your last period, and your average menstrual cycle (this is the number of days from the start of one period to the day before the next one), it's possible to estimate the date you conceived. Pregnancy is counted as being 40 weeks long, so your due date is calculated at 280 days from conception. Don't worry – our tool will do those sums for you, just fill in your info below and the results will show on our calendar.

How accurate are due dates?

At your 12-week scan (which can happen any time between 10 and 14 weeks), an ultrasound will be used to measure your baby and determine the stage of pregnancy you're at. The big date will then be confirmed with greater accuracy.

Remember, this date is not cast iron, but more an estimated due date at this stage. In fact, fewer than 5% of babies are born on the predicted day itself, but at least it gives you a rough deadline for buying the pushchair / painting the nursery / choosing a name.

How many weeks pregnant are you?

Based on the date your baby is due and/or the first day of your last period, you can count the number of weeks to see how pregnant you are. Once you know the magic number, find out what you can expect in the weeks ahead, using our pregnancy calendar.

6 weeks pregnant | 7 weeks pregnant | 8 weeks pregnant | 9 weeks pregnant | 10 weeks

Keep track of how your baby is developing week by week, the changes happening to your body and what appointments you'll have, as well as looking ahead to giving birth and life with a newborn (we know that part seems a long way off right now). In the meantime, chat with other mums-to-be who are at the same stage as you, by joining a birth club.