How many months pregnant am I? How to stop doing math wrong.

Someone told me recently that pregnancy is actually 10 months long, not 9, because it’s 40 weeks, and 40 weeks with 4 weeks per month = 10 months. If you Google “how many months pregnant is X weeks” you will get the same flawed math across the Internet.

Yes, folks. Flawed. I said it. Flawed. No, it’s not even flawed, it’s WRONG. I know that math is intimidating to some people, but I am here to help.

First, the 4 weeks in a month thing. Let’s debunk that. Stay with me, but here’s something you should be comfortable with: every week has 7 days. If you multiply 7 days*4 weeks…that will give you the amount of days that is. Which is….28. There is precisely one month in a year with 28 days: February. The rest have either 31 or 30 days. So far, I hope you are following me.

So let’s take this a little bit further.

Here are two other indisputable facts that don’t require math: there are 365 days in a year, and 12 months in a year. Now for the math. If you apportion those days out equally across the months (that’s 365 days/12 months) that comes out to…30.42 days per month. THAT is why some months are 30 days, some months are 31 days, and why February is 28 days – it’s to even out that .42 nonsense across 12 months (and it’s also why we need February to be 29 days every 4 years).

So if you go for 40 weeks of pregnancy…that’s 280 days. Divide that out by what we just learned, that across a year there are actually 30.42 days in a month (so that means divide 280/30.42)…that’s 9.2 months. Considering that full term is 37 weeks…you can do the same thing….37 * 7 = 259 (that’s the length of 27 weeks in days), then divide by 30.42 (the length of a month), and that’s 8.5 months.

So, on average, that means that pregnancy is anywhere from 8.5 – 9.2 months, which 9 months is a pretty good average.

Have I lost you?

Well, shoot. Let me make it up to you and give you a trick.

google_degree_conversionDid you know that Google has a native conversion tool in it? For instance, if you go to Google and type in “3 tablespoons in cups” or “5 meters in feet” or “18 degrees celsius in fahrenheit” Google actually will just do the conversion for you? Yup, that’s right. And it works for almost anything, INCLUDING WEEKS TO MONTHS.

Here’s what happened when I typed in: 22 weeks in months:


Ta da! Did I just make your life easier or what? So many people think that 22 weeks, well, 20 weeks is 5 months, then add 2 weeks, 5.5 months pregnant! But that’s wrong! I’m barely over 5 months pregnant (SERIOUSLY?!?!?).

If you prefer to do math the old way, then I will give you the formula, too. So taking all that we deduced before…here you go…here’s what you do:

(Number of weeks pregnant * 7) / 30.42

There ya go! Easy peasy.

So everyone, please, for the love of all that is real math, stop saying there are 4 weeks in a month and using that math to deduce how many months pregnant you are. 

Capiche? Okay, we’re cool now. Happy math-ing!

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