Pregnancy Due Date Calculator

This pregnancy calculator works out baby's due date for you! To calculate your due date, enter the date of your last period in the top box and click 'calculate' and we'll predict the due date of your baby, along with your trimester dates.

Frequently asked questions

What does this due date calculator tell me?

We’ve developed this tool to be as useful as possible. In addition to your estimated due date, this calculator will tell you:

• Your estimated date of conception
• How many weeks pregnant you are
• The date of each pregnancy trimester starting and finishing
• The star sign your baby will have (based on due date)
• Your baby’s birthstone
• Your baby’s birth flower

How to calculate your baby’s due date

To use our due date calculator, simply enter the date that your last period started, and we’ll calculate your due date and trimester dates for you!

A full term pregnancy is considered to be 38 weeks from the date of conception. However unless you’re tracking your ovulation, it’s unlikely you’re aware of the day you conceived. Most women ovulate around two weeks after the first day of the last menstrual period, and so medical practitioners (and this calculator) estimate your due date by adding 280 days (40 weeks) to the date of the start of your last period (LMP in medical-speak). That means the first two weeks of ‘pregnancy’ are actually counting your period and ovulation!

If you want to manually calculate your due date, the easiest way is to subtract three months from the date of your last period starting, then add seven days. For example, if your last period started on September 12th, then you’d subtract three months and add seven days to calculate June 19th as your estimated due date (the following year, obviously!)

If you do know your date of conception (if you’re tracking your ovulation, or are undergoing IVF), your due date can be calculated by adding 266 days to the conception date.

How accurate is my due date?

This calculator uses the same method to calculate your EDD (estimated due date) as your medical practitioner does before you have a dating scan, so it’s accurate in that it uses the same methodology as most healthcare providers.

However, growing a baby isn’t like ordering a product from Amazon, and every pregnancy is different. Only 5% of expectant women deliver their baby on their due date!

A typical pregnancy gestation lasts between 38 and 42 weeks, so it’s more of a due month than a due date! Only births that happen before the start of week 37 are considered ‘premature’ and high risk.

Each week of in-utero development helps ensure a stronger and fitter baby, and doctors now suggest that a “full term” birth after the start of week 39 is the ideal gestation period.

• Pre-term, before 37 weeks
• Early Term, between 37 weeks and 38 weeks 6 days.
• Full Term, between 39 weeks and 40 weeks 6 days.
• Late Term, the 41st week.
• Post Term, after 42 weeks.

Will my due date change at my dating scan?

Sometime between being 10 and 14 weeks pregnant you should be scheduled in for your first prenatal ultrasound scan, commonly known as a dating scan. This will be used by your midwife or medical practitioner to give you a more accurate due date, based on the observed development of your fetus including the length from head to bottom.

It’s also possible that your doctor might change your due date as your pregnancy progresses. This is normally not something to worry about, and may be due to an inaccurate dating scan, a particularly fast-developing fetus or a number of medical reasons.

What are trimesters?

A trimester literally means ‘three months’ - so essentially split your pregnancy into three trimesters of roughly equal length.

• First trimester - Weeks 1 to 13
• Second trimester - Weeks 14 to 26
• Third trimester - Weeks 27 to 40+

(Note that the dates of trimesters are rarely consistent between different sources; there are multiple ways of calculating trimesters. Read more on our ‘Pregnancy week by week’ page to discover why!)

Can I plan my due date?

Not once you’re pregnant! Although there are plenty of things you can try to encourage labour if you’re overdue.

If you’re actively trying to conceive or considering IVF, you can aim to time your conception by using our ovulation calendar. Just bear in mind that conception is a game of chance, and it’s unlikely you will be able to dictate exactly when you get pregnant!

What if I’m expecting twins?

The method of calculation for your expected due date is the same regardless of whether you’re expecting a single or multiple birth, although the average pregnancy for twins lasts around 35 weeks instead of 39-40 weeks for a single pregnancy.

Once you have your dating scan at around 12 weeks, the sonographer will use the size of the larger fetus to determine your due date.