How many weeks in 9 months? Pregnancy weeks to months calculator
A full-term pregnancy is counted as 40 weeks, which is about 9.2 calendar months. Nine calendar months is about 39 weeks (9 × 30.44 days ÷ 7 = 39.1 weeks). Pregnancy charts split the 40 weeks into nine pregnancy months instead. Use the calculator for your exact week, or scroll to the chart.
A calendar calculation, not medical advice. Your provider’s dating ultrasound is the reference for your due date. Nothing you type leaves this page.
How many weeks is 9 months of pregnancy?
About 39 weeks of calendar time, but pregnancy is dated from the first day of your last period, so the due date is set at 40 weeks (280 days). The two extra weeks at the start are why “nine months” and “40 weeks” both describe a full pregnancy.
| Pregnancy month | Weeks | Trimester |
|---|---|---|
| Month 1 | 1–4 | First |
| Month 2 | 5–8 | First |
| Month 3 | 9–13 | First |
| Month 4 | 14–17 | Second |
| Month 5 | 18–22 | Second |
| Month 6 | 23–27 | Second |
| Month 7 | 28–31 | Third |
| Month 8 | 32–35 | Third |
| Month 9 | 36–40 | Third |
Pregnancy weeks to months chart
| Week | Pregnancy month | Calendar months | Trimester |
|---|---|---|---|
| 1 | Month 1 | 0.2 | First |
| 2 | Month 1 | 0.5 | First |
| 3 | Month 1 | 0.7 | First |
| 4 | Month 1 | 0.9 | First |
| 5 | Month 2 | 1.1 | First |
| 6 | Month 2 | 1.4 | First |
| 7 | Month 2 | 1.6 | First |
| 8 | Month 2 | 1.8 | First |
| 9 | Month 3 | 2.1 | First |
| 10 | Month 3 | 2.3 | First |
| 11 | Month 3 | 2.5 | First |
| 12 | Month 3 | 2.8 | First |
| 13 | Month 3 | 3.0 | First |
| 14 | Month 4 | 3.2 | Second |
| 15 | Month 4 | 3.4 | Second |
| 16 | Month 4 | 3.7 | Second |
| 17 | Month 4 | 3.9 | Second |
| 18 | Month 5 | 4.1 | Second |
| 19 | Month 5 | 4.4 | Second |
| 20 | Month 5 | 4.6 | Second |
| 21 | Month 5 | 4.8 | Second |
| 22 | Month 5 | 5.1 | Second |
| 23 | Month 6 | 5.3 | Second |
| 24 | Month 6 | 5.5 | Second |
| 25 | Month 6 | 5.7 | Second |
| 26 | Month 6 | 6.0 | Second |
| 27 | Month 6 | 6.2 | Second |
| 28 | Month 7 | 6.4 | Third |
| 29 | Month 7 | 6.7 | Third |
| 30 | Month 7 | 6.9 | Third |
| 31 | Month 7 | 7.1 | Third |
| 32 | Month 8 | 7.4 | Third |
| 33 | Month 8 | 7.6 | Third |
| 34 | Month 8 | 7.8 | Third |
| 35 | Month 8 | 8.0 | Third |
| 36 | Month 9 | 8.3 | Third |
| 37 | Month 9 | 8.5 | Third |
| 38 | Month 9 | 8.7 | Third |
| 39 | Month 9 | 9.0 | Third |
| 40 | Month 9 | 9.2 | Third |
| 41 | Past 40 weeks | 9.4 | Third |
| 42 | Past 40 weeks | 9.7 | Third |
How the calculator counts
- Weeks are counted from the first day of your last menstrual period (LMP), the way providers date a pregnancy.
- The estimated due date is LMP + 280 days (40 weeks).
- Calendar months use the average month length of 30.44 days.
- Trimesters follow ACOG: the first runs through 13 weeks 6 days, the second from 14 through 27 weeks 6 days, and the third from week 28.
Questions
How many months is 40 weeks pregnant?
About 9.2 calendar months. On a pregnancy chart, week 40 is the end of month 9.
The 5th month is how many weeks?
Weeks 18 to 22 on a standard pregnancy chart, so 20 weeks falls in the middle of month 5.
How many weeks is 4 months pregnant?
Month 4 covers weeks 14 to 17. Four calendar months is about 17.4 weeks.
How many weeks is 6 months pregnant?
Month 6 covers weeks 23 to 27. Six calendar months is about 26.1 weeks.
When does the third trimester start?
At 28 weeks, according to ACOG’s trimester definitions.
Print the chart
The printable pregnancy planner includes this chart, trimester calendars, an appointment log and a 40-week countdown.
Sources
This page explains calendar math. It isn’t medical advice.