Pregnancy due date calculator

How to use this tool

1. Choose how you want to date the pregnancy: last period, conception date or IVF transfer.
2. Enter the date and, for the last period method, your usual cycle length.
3. Read the estimated due date and the current week of pregnancy.
4. Look at the key milestones and keep the dates for your appointments.

How it works

Due date = first day of last period + 280 days (40 weeks), plus or minus the difference from a 28-day cycle
From conception: conception date + 266 days
IVF day-5 transfer: transfer date + 261 days, day-3 transfer: + 263 days

This is Naegele's rule, the standard first estimate. A dating ultrasound in the first trimester is more accurate than a remembered period date, so follow your doctor's dates if they differ.

Good to know

A due date is an estimate. Only about 4 in 100 babies arrive on the exact day, and most are born within two weeks either side. Doctors usually date a pregnancy from the first day of the last period and then confirm it with an early ultrasound, which can adjust the date.

The calculator adds 280 days (40 weeks) to the start of the last period, adjusted for cycles longer or shorter than 28 days. For conception dates it adds 266 days, and for IVF it counts from the transfer date and the age of the embryo. This tool gives general information and is not medical advice. Talk to your midwife or doctor about your own care.