About Pregnancy Weeks to Months
Everyone you meet asks how many months along you are. Every appointment, test and scan is scheduled in weeks. The two do not line up, because a month is not four weeks — it averages 4.35.
This converter does the translation both ways, using the grouping antenatal clinics actually use.
How it works
Enter the week you are in, or the month, and the converter gives you the other along with the trimester.
| Weeks | Month | Trimester |
|---|---|---|
| 1–4 | 1 | First |
| 5–8 | 2 | First |
| 9–13 | 3 | First |
| 14–17 | 4 | Second |
| 18–22 | 5 | Second |
| 23–27 | 6 | Second |
| 28–31 | 7 | Third |
| 32–35 | 8 | Third |
| 36–40 | 9 | Third |
Weeks are written as "weeks + days": 24+3 means 24 weeks and 3 days. That precision matters for growth measurements and for anything time-critical, which is why clinics never switch to months.
Examples
The conversions people look up most:
- Week 12 — month 3, end of the first trimester, and usually the first scan.
- Week 20 — month 5, halfway, and the anatomy scan.
- Week 28 — month 7, the start of the third trimester.
- Week 37 — month 9, and the point at which a baby counts as full term.
To work out which week you are in from a date, use the due date calculator.
Pregnancy Weeks to Months: frequently asked questions
- Is 40 weeks nine months or ten?
Nine calendar months and about a week. The 'ten months' version counts lunar months of exactly 28 days, which is where the confusion comes from.
- Which weeks are the second trimester?
Weeks 14 to 27. Some sources start it at 13 weeks; the difference is a labelling convention, not a medical one.
- How many months is 30 weeks?
Month 7, in the third trimester, with about ten weeks to go.
- Why does the count start before conception?
Because pregnancy is dated from the last period, which is roughly two weeks earlier. It keeps dating consistent for everyone, whether or not the conception date is known.