Pregnancy weeks to months
Pregnancy is measured in weeks, but most people talk about months. Because a calendar month is about 4.3 weeks, the weeks do not divide evenly, and different books group them slightly differently. This pregnancy month calculator uses the most common grouping:
| 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 |
Common questions
- 29 weeks pregnant is how many months? Month 7 — see 29 weeks pregnant.
- 20 weeks is month 5, the halfway point of pregnancy.
- 40 weeks is the end of month 9 — slightly more than nine calendar months, because pregnancy is counted from the last period.
Why pregnancy months are confusing
There are three common ways to count months of pregnancy. Calendar months (about 4.3 weeks each) give a little over nine months. “Lunar months” of exactly four weeks give ten months of 28 days. And some people count from conception rather than the last period, which makes every month two weeks later. Books, apps and clinics may use any of these, so the same week can be described as month 6 in one place and month 7 in another. Weeks are unambiguous, which is why your care team uses them — this calculator shows both so you can translate between them.
For your exact week and day, use the Pregnancy Week Calculator; for trimester dates, the Trimester Calculator.