Pregnancy Weeks to Months: How to Do the Math Accurately

You know your due date, but how many weeks pregnant are you? What about months? This guide will help you convert pregnancy weeks to months.

Pregnancy Weeks to Months-MAIN

If you just found out that you’re expecting, one of your first questions is likely how far along am I? Knowing how many weeks pregnant you are helps you track your milestones and count down to your due date. But pregnancy math can be a bit confusing, especially when you try to convert pregnancy weeks to months. Don’t worry: We’ll break it all down for you.

Pregnancy Weeks to Months

Tracking pregnancy weeks is easy—you simply count up from the first day of your last menstrual period.

But converting pregnancy weeks to months? That’s tricky, because there’s only one month with exactly four full weeks, and that’s February. January, March, May, July, August, October, and December all have 31 days, which means the average month has four full weeks, plus a few extra days.

Since one month doesn’t really equal four weeks—it’s just a rough estimate—simply dividing by four doesn’t give you the most accurate answer. And during pregnancy, accuracy is key in order to get the best representation of your baby’s growth.

Still, inquiring folks may still ask “how many months are you?” In this case, it’s fine to use four weeks as your dividing factor. Here’s a quick cheat sheet for you:

How many months is…

8 weeks pregnant?

If you’re 8 weeks pregnant, you are two months pregnant. This means you have completed two months (8 weeks) and are working your way through your third month.

9 weeks pregnant?

If you’re 9 weeks pregnant, you are two months and one week pregnant.

10 weeks pregnant?

If you’re 10 weeks pregnant, you are two months and two weeks pregnant, or 2.5 months.

11 weeks pregnant?

If you are 11 weeks pregnant, you are two months and three weeks pregnant.

12 weeks pregnant?

If you are 12 weeks pregnant, you are three months pregnant.

13 weeks pregnant?

If you are 13 weeks pregnant, you are three months and one week pregnant.

14 weeks pregnant?

You’ve made it to the second trimester! If you are 14 weeks pregnant, you are three months and two weeks pregnant, or 3.5 months. This is a great time to start drinking red raspberry leaf tea.

15 weeks pregnant?

If you are 15 weeks pregnant, you are three months and three weeks pregnant.

16 weeks pregnant?

If you are 16 weeks pregnant, you are four months pregnant.

17 weeks pregnant?

If you are 17 weeks pregnant, you are four months and one week pregnant.

18 weeks pregnant?

If you are 18 weeks pregnant, you are four months and two weeks pregnant, or 4.5 months.

19 weeks pregnant?

If you are 19 weeks pregnant, you are four months and three weeks pregnant.

20 weeks pregnant?

If you are 20 weeks pregnant, you are five months pregnant. This is also when many mamas go in for their anatomy scan.

21 weeks pregnant?

If you are 21 weeks pregnant, you are five months and one week pregnant. This is a good time to sign up for a childbirth education class.

22 weeks pregnant?

If you are 22 weeks pregnant, you are five months and two weeks pregnant, or 5.5 months.

23 weeks pregnant?

If you are 23 weeks pregnant, you are five months and three weeks pregnant.

24 weeks pregnant?

If you are 24 weeks pregnant, you are six months pregnant.

25 weeks pregnant?

If you are 25 weeks pregnant, you are six months and one week pregnant.

26 weeks pregnant?

If you are 26 weeks pregnant, you are six months and two weeks pregnant, or 6.5 months.

27 weeks pregnant?

If you are 27 weeks pregnant, you are six months and three weeks pregnant.

28 weeks pregnant?

Welcome to the third trimester! You are seven months pregnant!

29 weeks pregnant?

If you are 29 weeks pregnant, you are seven months and one week pregnant.

30 weeks pregnant?

If you are 30 weeks pregnant, you are seven months and two weeks pregnant, or 7.5 months.

31 weeks pregnant?

If you are 31 weeks pregnant, you are seven months and three weeks pregnant.

32 weeks pregnant?

If you are 32 weeks pregnant, you are eight months pregnant.

33 weeks pregnant?

If you are 33 weeks pregnant, you are eight months and one week pregnant.

34 weeks pregnant?

If you are 34 weeks pregnant, you are eight months and two weeks pregnant, or 8.5 months.

35 weeks pregnant?

If you are 35 weeks pregnant, you are eight months and three weeks pregnant.

36 weeks pregnant?

If you are 36 weeks pregnant, you are nine months pregnant! This is when you should start eating your dates for a faster birth!

37 weeks pregnant?

If you are 37 weeks pregnant, you are nine months and one week pregnant. This is also when you are “cleared” to have a home birth, if that is your desire.

38 weeks pregnant?

If you are 38 weeks pregnant, you are nine months and two weeks pregnant, or 9.5 months pregnant.

39 weeks pregnant?

If you are 39 weeks pregnant, you are nine months and three weeks pregnant.

40 weeks pregnant?

Congrats! You’ve reached the end of pregnancy. You are 10 months pregnant. (More on this in a moment!) Now be on the lookout for signs of labor! If you are looking for natural induction ideas, check out this article.

Pregnancy Weeks to Months Chart

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So Is Pregnancy 9 or 10 Months?

We know pregnancy is 280 days, or 40 weeks, but how many months is it? Is it nine months? Or ten, as mentioned above? Let’s take a look at the math:

  • 40 weeks divided by 4 weeks is 10 months.
  • 40 weeks divided by 4.3 weeks (the length of the average month, as referenced above) is 9.3 months.
  • 280 days divided by 30 (average days in a month) is 9.3 months.

So which formula is right?! Technically, they all are!

How is that possible?

While your due date and the amount of time you’re pregnant doesn’t change, it’s the language being used that changes. Pregnancy is—on average—40 weeks, no matter what formula you use.

Figuring out the pregnancy weeks to months, on the other hand, depends on what number you’re using for the length of a month. When you use four, pregnancy seems to be 10 months. When you use the average number of days in a month, pregnancy is closer to nine months.

Pregnancy Trimesters

To make it even more confusing, months and weeks aren’t the only way to track your pregnancy. Trimesters are also important markers during pregnancy. So what weeks fall under what trimesters? Let’s break it down:

First Trimester

The first trimester begins on the first day of your last menstrual period and consists of 13 full weeks.

Pregnancy Charts – First Trimester

Second Trimester

The second trimester begins at the start of your 14th week. This trimester consists of 13 full weeks.

Pregnancy Charts – Second Trimester

Third Trimester

The third trimester begins after you’ve completed your 27th week, or at the start of your 28th week. This trimester is an outlier, lasting 14+ weeks.

Pregnancy Charts – Third Trimester

How Many Weeks Am I?

So here’s the big question: how many weeks are YOU? Use our due date calculator to find out. And don’t forget to bookmark this pregnancy weeks to months cheat sheet—you’ll need it!

Genevieve Howland

About the Author

Genevieve Howland is a childbirth educator and breastfeeding advocate. She is the bestselling author of The Mama Natural Week-by-Week Guide to Pregnancy and Childbirth and creator of the Mama Natural Birth Course. A mother of three, graduate of the University of Colorado, and YouTuber with over 85,000,000 views, she helps mothers and moms-to-be lead healthier and more natural lives.

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