How do pregnancy weeks convert to months?
A pregnancy lasts 40 weeks from the first day of your last period, and most guides split those 40 weeks into nine months: weeks 1–4 are the 1st month, 5–8 the 2nd, 9–13 the 3rd, 14–17 the 4th, 18–22 the 5th, 23–27 the 6th, 28–31 the 7th, 32–35 the 8th and 36–40 the 9th. Because months don't divide evenly into weeks, some months have four weeks and some have five.
Pregnancy weeks to months chart
| Month | Weeks | Trimester |
|---|---|---|
| 1st month | 1–4 | first |
| 2nd month | 5–8 | first |
| 3rd month | 9–13 | first, then second from week 13 |
| 4th month | 14–17 | second |
| 5th month | 18–22 | second |
| 6th month | 23–27 | second, then third from week 27 |
| 7th month | 28–31 | third |
| 8th month | 32–35 | third |
| 9th month | 36–40 | third |
Each week page shows the month it falls in. To find your week first, use how many weeks pregnant am I, or the due date calculator if you want the date too.
How many weeks is 6 months pregnant?
Six months pregnant is weeks 23 to 27. You enter the 6th month at 23 weeks and finish it at the end of week 27. By calendar months, 6 full months is about 26 weeks.
Week by week: 23 weeks, 24 weeks, 25 weeks, 26 weeks, 27 weeks.
How many weeks is 7 months pregnant?
Seven months pregnant is weeks 28 to 31. You enter the 7th month at 28 weeks and finish it at the end of week 31. By calendar months, 7 full months is about 30 weeks.
How many weeks is 8 months pregnant?
Eight months pregnant is weeks 32 to 35. You enter the 8th month at 32 weeks and finish it at the end of week 35. By calendar months, 8 full months is about 35 weeks.
How many weeks is 9 months pregnant?
Nine months pregnant is weeks 36 to 40. You enter the 9th month at 36 weeks and finish it at the end of week 40. The 9th month runs to your due date at 40 weeks, and many babies arrive in the weeks either side of it.
Week by week: 36 weeks, 37 weeks, 38 weeks, 39 weeks, 40 weeks.
How many weeks is 5 months pregnant?
Five months pregnant is weeks 18 to 22. You enter the 5th month at 18 weeks and finish it at the end of week 22. By calendar months, 5 full months is about 22 weeks.
Week by week: 18 weeks, 19 weeks, 20 weeks, 21 weeks, 22 weeks.
How many weeks is 4 months pregnant?
Four months pregnant is weeks 14 to 17. You enter the 4th month at 14 weeks and finish it at the end of week 17. By calendar months, 4 full months is about 17 weeks.
How many weeks is 3 months pregnant?
Three months pregnant is weeks 9 to 13. You enter the 3rd month at 9 weeks and finish it at the end of week 13. By calendar months, 3 full months is about 13 weeks.
Week by week: 9 weeks, 10 weeks, 11 weeks, 12 weeks, 13 weeks.
Why “months pregnant” doesn't have one answer
A calendar month averages about 4.3 weeks, so 40 weeks works out to about 9.2 calendar months. Count in four-week blocks instead and 40 weeks is exactly 10 of them, which is where you sometimes hear that pregnancy is really ten months long. The nine-month chart above is a third way of counting, and it's the one most pregnancy guides use.
There's also a difference between being in a month and having completed it. At 23 weeks you're in your 6th month, but you've only completed about five calendar months. That's why two websites can give you different answers to the same question, and why doctors, midwives and scan reports use weeks and days instead. If your provider has given you dates from an ultrasound, go by those.
Pregnancy week by week
Once you know how far along you are, each week's guide covers your baby's size and development, common symptoms, and what to do that week.
Frequently asked questions
Sources and medical references
Pregnancy is counted in weeks from the last period, as described in ACOG's guidance on estimating the due date and by the NHS and Mayo Clinic. The grouping into months is a convention, not a clinical standard.