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Pregnancy due date calculator

Find your estimated due date and how many weeks pregnant you are today.

Work it out from
The day your last period started.
From the start of one period to the start of the next. Use 28 if you're not sure.

This is an estimate. Your midwife or doctor will confirm your due date, usually at your first scan. Only a small share of babies arrive on their due date.

Nothing you type here is saved or sent anywhere.

How this is worked out

From the first day of your last period, the due date is 280 days (40 weeks) later. This is Naegele's rule, the standard starting point. If your cycle is longer or shorter than 28 days, the date moves by the difference, because ovulation usually happens later or earlier.

From a known conception date, the due date is 266 days later. After IVF it is 263 days after a 3-day embryo transfer, or 261 days after a 5-day transfer.

How far along you are is counted the same way clinics count it: from the first day of your last period, so the weeks include about two weeks before conception. These day counts follow the American College of Obstetricians and Gynecologists' guidance on estimating the due date (Committee Opinion 700).

What this doesn't account for

  • Irregular cycles. If your cycle length varies a lot, the date from your period is less reliable, and the dating scan matters more.
  • Your dating scan. When a scan measurement differs from your period date, clinics usually go by the scan.
  • Twins and other multiple pregnancies, which often arrive earlier.
  • Your health and history. Only your midwife or doctor can take those into account.

Common questions

How accurate is a due date calculator?

It gives an estimate, worked out the same way midwives and doctors start. Only a small share of babies arrive on their due date. Most arrive between 37 and 42 weeks, and the dating scan usually gives a more accurate date.

How many weeks pregnant am I?

Pregnancy is counted from the first day of your last period, not from conception, so you are already about 2 weeks pregnant at conception. Enter that date above to see your weeks and days today.

Can my due date change?

Yes. If the measurements at your dating scan point to a different date from your period, your midwife or doctor may give you a new due date based on the scan.

What if I don't know the date of my last period?

Use your conception date if you know it. If not, your dating scan will estimate how far along you are from the baby's size.

How is an IVF due date worked out?

From the transfer date: add 263 days for a 3-day embryo or 261 days for a 5-day embryo. Both are the same as counting 266 days from egg collection.

When should I talk to a midwife or doctor?

Contact a midwife, GP or doctor as soon as you know you are pregnant so your care can be arranged. Get urgent help for bleeding, strong pain or anything that worries you.