Weeks to months pregnancy calculator
Convert any pregnancy week into months — and back — in one tap, with the trimester and where you are in the 40-week journey. Weeks-to-months is one of the most confusing parts of pregnancy because a pregnancy "month" isn't a tidy four weeks: 40 weeks spread across nine months means each month runs a little over four weeks. This tool does the math for you and shows the full reference chart below.
Type a number above to see the breakdown.
How pregnancy weeks map to months
Pregnancy is counted in weeks from the first day of your last menstrual period, and a full term lasts about 40 weeks. Those 40 weeks are grouped into nine months — but a pregnancy month averages roughly 4.3 weeks, not a flat four. That small gap is why the numbers never line up cleanly: 40 weeks divided into four-week blocks would be ten, yet on the calendar it works out to about nine months.
Doctors and midwives count almost everything in weeks because it's far more precise than calendar months — a single week marks real milestones in your baby's development. The chart below maps every week from 1 to 42 to its month and trimester so you can switch between the two whenever a friend, app, or appointment uses the one you're less used to. Month boundaries follow standard obstetric guidance (ACOG, WHO); this tool is for general information and is not medical advice.
Pregnancy weeks-to-months chart
A general reference for every week of pregnancy, 1 to 42 — independent of the calculator above.
| Weeks | Month | Trimester |
|---|---|---|
| 1 weeks | Month 1, week 1 | T1 |
| 2 weeks | Month 1, week 2 | T1 |
| 3 weeks | Month 1, week 3 | T1 |
| 4 weeks | Month 1, week 4 | T1 |
| 5 weeks | Month 2, week 1 | T1 |
| 6 weeks | Month 2, week 2 | T1 |
| 7 weeks | Month 2, week 3 | T1 |
Common questions
Pregnancy months are measured in weeks counted from the first day of your last period, then grouped so the full 40-week term spans nine months. Because each month covers a little more than four weeks, month 1 is weeks 1–4, but later months stretch to five weeks — month 6, for example, runs weeks 22–26.
Your care team tracks gestational age in weeks, which is more exact than calendar months and starts two weeks before conception (from your last period). "Months pregnant" rounds that same timeline into bigger blocks, so the two can look out of step — at 30 weeks you're roughly seven months along, even though 30 ÷ 4 suggests seven and a half.
Due dates are set at 40 weeks, but a baby is considered full-term any time from 37 to 42 weeks. Births before 37 weeks are preterm, and pregnancies are rarely allowed to continue past 42 weeks, so this calculator covers the full 1–42 week range.
Both numbers are correct — they just use different "months." Across the calendar, 40 weeks works out to about nine months. If you count in lunar months of exactly four weeks each, 40 weeks is ten. The nine-month figure is the everyday one; the ten-month version is why pregnancy can feel longer than expected.
The first trimester runs weeks 1–13, the second covers weeks 14–26, and the third spans weeks 27 to birth. Each lasts roughly three months, and many milestones — like the end of early symptoms or the start of the home stretch — line up with these boundaries.
24 weeks is in month 6 of pregnancy, in the second trimester. Month 6 covers weeks 22–26, so at 24 weeks you're partway through it and around the halfway-to-two-thirds point of the whole pregnancy.
Medical Disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or qualified health provider with any questions you may have regarding a medical condition.
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