Weeks to Months

Convert pregnancy weeks into months. This free weeks-to-months pregnancy converter shows the matching month and trimester for any week, with a complete reference chart.

A simple guide to how pregnancy weeks line up with months. Pregnancy is officially tracked in weeks because 40 weeks is a little longer than nine calendar months, so month boundaries are approximate.
Weeks pregnant

Enter how many weeks (and optional extra days) you are. The converter shows the equivalent pregnancy month and trimester using the standard reference.

Pregnancy month
—
Enter your weeks
Trimester
—
Weeks + days
—
Total days
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Weeks to 40
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Common reference: month 1 = weeks 1–4, month 2 = 5–8, month 3 = 9–13, month 4 = 14–17, month 5 = 18–22, month 6 = 23–27, month 7 = 28–31, month 8 = 32–35, month 9 = 36–40.

Use this free weeks to months pregnancy converter to turn your pregnancy weeks into months. Enter your weeks and it shows the matching month and trimester using the standard reference.

What this weeks to months converter does

This weeks to months pregnancy tool converts how many weeks pregnant you are into the equivalent pregnancy month and trimester. It’s handy because pregnancy is tracked in weeks, but people often think in months.

Pregnancy weeks to months chart

Month Weeks Trimester
1 1 – 4 First
2 5 – 8 First
3 9 – 13 First
4 14 – 17 Second
5 18 – 22 Second
6 23 – 27 Second
7 28 – 31 Third
8 32 – 35 Third
9 36 – 40 Third

Why isn’t it exactly 9 months?

A full-term pregnancy is about 40 weeks, which is roughly nine calendar months plus a week or so. Because months vary in length, the week-to-month mapping is approximate — which is exactly why doctors count in weeks.

How to use the converter

  1. Enter your weeks (and extra days if you like).
  2. Read the pregnancy month and trimester.
  3. See total days and weeks remaining to 40.

Weeks to Months FAQ

How do I convert pregnancy weeks to months?

Use the standard mapping: weeks 1–4 are month 1, 5–8 month 2, 9–13 month 3, and so on. Enter your weeks and the converter shows the month and trimester.

How many months is 20 weeks pregnant?

20 weeks falls in month 5 and the second trimester — roughly the halfway point of pregnancy.

How many months is 28 weeks pregnant?

28 weeks is the start of month 7 and the third trimester.

Why is pregnancy 40 weeks but only 9 months?

40 weeks is about nine calendar months plus a week or so. Months differ in length, so weeks give a more precise count — which is why clinicians use them.

Are the month boundaries exact?

They're a widely used approximation. Different charts vary slightly, but this one follows the common reference used by pregnancy resources.

Is the weeks to months converter free?

Yes, this weeks to months pregnancy converter is completely free, needs no sign-up, and works instantly in your browser.

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