Month 1 of Pregnancy Is How Many Weeks?

"Pregnancy Weeks to Months" Calculator

Month 1 of Pregnancy Is How Many Weeks?

Answer

Month 1 of Pregnancy is

1–4 Weeks

First trimester

Obstetric months and calendar months

Doctors count in obstetric months of exactly four weeks. By that count 1–4 Weeks is the 1st obstetric month.

A calendar month averages 30.4375 days, so the same term is about 0.23–0.92 calendar months. The two counts never agree, and by the end of a term they differ by 0.8 of a month: 40 weeks are 10 obstetric months and 9.2 calendar ones.

Which weeks this month covers

About "Pregnancy Weeks to Months" Calculator

Pregnancy is counted in completed weeks from the first day of the last menstrual period, and a full term is 40 weeks or 280 days — that is Naegele's rule. Enter a term in weeks and the calculator says which obstetric month it falls into, which trimester it belongs to, how many weeks are left and when the estimated due date is.

An obstetric month is exactly four weeks, which is why 40 weeks make ten obstetric months but only about nine calendar ones. Both numbers are printed on every page, because the two counts disagree and the disagreement is what the question is usually about.

This is an arithmetic tool, not medical advice. The due date it prints is an estimate; only a doctor can set the real term.

"Pregnancy Weeks to Months" Calculator

Pregnancy Weeks and Months Table

Month of Pregnancy	Weeks of Pregnancy	Trimester
1 Month	1–4 Weeks	First trimester
2 Months	5–8 Weeks	First trimester
3 Months	9–12 Weeks	First trimester
4 Months	13–16 Weeks	First–second trimester
5 Months	17–20 Weeks	Second trimester
6 Months	21–24 Weeks	Second trimester
7 Months	25–28 Weeks	Second–third trimester
8 Months	29–32 Weeks	Third trimester
9 Months	33–36 Weeks	Third trimester

Month 1 of Pregnancy Is How Many Weeks