When is my baby due?
Add 280 days (40 weeks) to the first day of your last period. If your cycle is longer or shorter than 28 days, shift by the difference. If you know the conception date, add 266 days. Your dating scan sets the final date.
Enter a date to calculate.
Everything is calculated on your own device. We store nothing and send nothing anywhere.
This is an estimate, not medical advice and not contraception. If in doubt, ask your GP or midwife.
How we calculate
We use Naegele's rule: the first day of your last period plus 280 days, adjusted for your cycle length. From conception it is 266 days.
How certain is the date?
Only a small share of babies arrives exactly on the due date. A birth between 37 and 42 weeks counts as on time. The dating scan at around 10 to 14 weeks gives the most accurate date.
What next?
Contact your midwife or GP to book your first appointment.
Want to know every month, without the maths?
PERIOD. learns from your own cycles and keeps your predictions up to date. Free, no ads, and we never sell your data.
Frequently asked questions
How is a due date calculated?
The first day of your last period plus 280 days. With a cycle longer or shorter than 28 days you shift by the difference.
How accurate is a due date?
It is an estimate. A birth between 37 and 42 weeks counts as on time, and the dating scan sets the date most accurately.
Can I calculate from conception?
Yes, add 266 days to the conception date. Choose "Conception date" above.
When is the dating scan?
Usually at around 10 to 14 weeks of pregnancy. Your midwife or GP books it with you.
Read more
Other free tools
Sources: NHS, Periods and fertility in the menstrual cycle; NHS, Pregnancy due date; ACOG, Methods for estimating the due date.