How it is calculated
Naegele's rule: last period date plus 280 days (40 weeks), adjusted if your cycle is not 28 days.
Important
It is only an estimate. Few babies are born exactly on that day. Your doctor will confirm the date with an ultrasound.
Frequently asked questions
How long is a pregnancy?
About 40 weeks from the last period.
What if my cycle is irregular?
Your doctor can adjust the date with an ultrasound.
When does each trimester start?
The second at week 14 and the third at week 28.
Does it replace a medical visit?
No.
What is LMP?
The first day of your last menstrual period.