Question 1

How is the due date calculated?

Accepted Answer

The due date is calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If you know your conception date, add 266 days (38 weeks) to that date.

Question 2

How accurate is the due date estimate?

Accepted Answer

Only about 5% of babies are born on their exact due date. Most are born within two weeks before or after. The estimate is most accurate when based on an early ultrasound, but LMP-based calculation is a reliable starting point.

Question 3

What are the three trimesters?

Accepted Answer

The first trimester spans weeks 1-13, the second trimester spans weeks 14-27, and the third trimester spans weeks 28-40. Each trimester marks different developmental milestones for the baby.

Question 4

Can I use IVF transfer date instead?

Accepted Answer

Yes. For IVF, if you had a Day 5 embryo transfer, add 261 days to the transfer date. For a Day 3 transfer, add 263 days. This gives the same due date as a natural conception calculation.