At 20 weeks you are 4.6 months pregnant, in month 5 and the second trimester. The third trimester starts at 28 weeks, or 6.4 months.
General information, not medical advice. Read the disclaimer
| Week | Days | Months completed | Month of pregnancy | Trimester | Weeks to due date |
|---|---|---|---|---|---|
| 1 | 7 | 0.2 | 1 | First | 39 |
| 2 | 14 | 0.5 | 1 | First | 38 |
| 3 | 21 | 0.7 | 1 | First | 37 |
| 4 | 28 | 0.9 | 1 | First | 36 |
| 5 | 35 | 1.1 | 2 | First | 35 |
| 6 | 42 | 1.4 | 2 | First | 34 |
| 7 | 49 | 1.6 | 2 | First | 33 |
| 8 | 56 | 1.8 | 2 | First | 32 |
| 9 | 63 | 2.1 | 3 | First | 31 |
| 10 | 70 | 2.3 | 3 | First | 30 |
| 11 | 77 | 2.5 | 3 | First | 29 |
| 12 | 84 | 2.8 | 3 | First | 28 |
| 13 | 91 | 3.0 | 3 | First | 27 |
| 14 | 98 | 3.2 | 4 | Second | 26 |
| 15 | 105 | 3.4 | 4 | Second | 25 |
| 16 | 112 | 3.7 | 4 | Second | 24 |
| 17 | 119 | 3.9 | 4 | Second | 23 |
| 18 | 126 | 4.1 | 5 | Second | 22 |
| 19 | 133 | 4.4 | 5 | Second | 21 |
| 20 | 140 | 4.6 | 5 | Second | 20 |
How it is computed
Weeks count from the first day of the last menstrual period, with the due date at 40 weeks (280 days). Months = days ÷ 30.44, the average calendar month. Trimesters follow ACOG: first through week 13, second from week 14 to 27, third from week 28.
FAQ
Is pregnancy 9 months or 10?+
40 weeks is about 9.2 calendar months counted from the last period, which is why it is called nine months; counting four-week months gives ten.
Why are weeks counted from my last period?+
Conception is hard to date, while the last period is usually known, so doctors date pregnancy from it; conception is about two weeks later.