Question 1

How accurate is the due date calculation?

Accepted Answer

Naegele's rule gives a statistical estimate; only about 5% of babies are born on their exact EDD. Most arrive within 2 weeks either side. First-trimester ultrasound is more accurate when dates are uncertain.

Question 2

What if my cycle is not 28 days?

Accepted Answer

Adjust the EDD by the difference: if your cycle is 35 days, add 7 days to the standard EDD. Ultrasound dating in the first trimester bypasses this issue.

Question 3

When do trimesters start and end?

Accepted Answer

First: weeks 1–13. Second: weeks 14–26. Third: weeks 27–40. "Weeks pregnant" counts from the LMP, not conception, so you are already "2 weeks pregnant" before ovulation.

Question 4

What is a term pregnancy?

Accepted Answer

Full term is 39–40 weeks. Early term is 37–38 weeks. Late term is 41 weeks. Post-term is 42+ weeks. Births before 37 weeks are considered preterm.

Question 5

Does the due date change after an early scan?

Accepted Answer

Yes — if the scan date differs from the LMP-based EDD by more than 5–7 days (first trimester), the scan date usually takes precedence as the new EDD.

Pregnancy Due Date Calculator — Free Online Calculator