Pregnancy Weeks to Months Calculator
Doctors count pregnancy in weeks; friends ask in months. Convert any week to its month and trimester.
Keep your dates in Prego: a daily countdown, your baby's size each week and a checklist for every trimester.
Pregnancy weeks to months chart
| Month | Weeks | Trimester |
|---|---|---|
| Month 1 | 1 to 4 | First |
| Month 2 | 5 to 8 | First |
| Month 3 | 9 to 13 | First |
| Month 4 | 14 to 17 | Second |
| Month 5 | 18 to 22 | Second |
| Month 6 | 23 to 27 | Second |
| Month 7 | 28 to 31 | Third |
| Month 8 | 32 to 35 | Third |
| Month 9 | 36 to 40+ | Third |
A 40-week pregnancy is a little over nine calendar months. Because months aren't all the same length, different sources split the weeks slightly differently. This chart uses the most common split, where each trimester is three months.
Frequently asked questions
How many months is 40 weeks pregnant?
Forty weeks is the end of month nine. Counted from your last period, a full-term pregnancy is about nine months and one week.
Is 4 weeks one month pregnant?
Yes. Weeks 1 to 4 make up the first month, so at 4 weeks you are at the end of month one, around the time your period is due.
What weeks are each trimester?
The first trimester is weeks 1 to 13, the second is weeks 14 to 27 and the third is week 28 until birth.
Estimates only. Your doctor or midwife may give you different dates or targets.