How the Pregnancy Month Calculator works
The calculator first works out your exact gestational age in weeks and days — from the first day of your last period or from your due date — and then places it in the matching month of pregnancy. The result shows your month, week, trimester and estimated due date, and the range of weeks and dates that make up your current month.
Pregnancy weeks to months
This site uses the common nine-month grouping below. Each month links to a page explaining what typically happens during it.
| Pregnancy month | Weeks pregnant (completed) | Trimester |
|---|---|---|
| Month 1 | Weeks 1–4 | First |
| Month 2 | 5 to 8 weeks | First |
| Month 3 | 9 to 13 weeks | First |
| Month 4 | 14 to 17 weeks | Second |
| Month 5 | 18 to 22 weeks | Second |
| Month 6 | 23 to 27 weeks | Second |
| Month 7 | 28 to 31 weeks | Third |
| Month 8 | 32 to 35 weeks | Third |
| Month 9 | 36 to 40 weeks | Third |
Why pregnancy weeks are more precise than months
Calendar months vary from 28 to 31 days, while pregnancy is measured in exact days from a fixed starting point. A 40-week pregnancy is 280 days — about 9.2 calendar months — so there is no perfect way to split it into nine months. Some sources start month 4 at 13 weeks, others at 14; some count ten four-week months. None of these is wrong, but they disagree at the edges.
Weeks avoid that problem. They are what your healthcare professional uses, what an ultrasound reports, and what determines when tests are offered — the anatomy scan around 18–22 weeks or glucose screening around 24–28 weeks, for example. Think of the month as a friendly shorthand, and the week as the precise answer. The Pregnancy Week Calculator gives that answer in weeks and days.
Months and trimesters
Each trimester is roughly three months: months 1–3 are the first trimester (to 13 weeks 6 days), months 4–6 the second (14 to 27 weeks 6 days), and months 7–9 the third (28 weeks to birth). Month 9 often stretches past a calendar month because babies are commonly born anywhere between 37 and 42 weeks. The Trimester Calculator shows the exact dates of each of your trimesters.
Month-by-month guides
Month 1Month 2Month 3Month 4Month 5Month 6Month 7Month 8Month 9