Convert pregnancy weeks into months. This free weeks-to-months pregnancy converter shows the matching month and trimester for any week, with a complete reference chart.
Enter how many weeks (and optional extra days) you are. The converter shows the equivalent pregnancy month and trimester using the standard reference.
Common reference: month 1 = weeks 1–4, month 2 = 5–8, month 3 = 9–13, month 4 = 14–17, month 5 = 18–22, month 6 = 23–27, month 7 = 28–31, month 8 = 32–35, month 9 = 36–40.
How This Weeks-to-Months Converter Works
Enter how many weeks pregnant you are, plus any extra days if you know them, and the converter instantly shows the matching pregnancy month, trimester, total days, weeks-plus-days format, and how many weeks remain until the traditional 40-week mark. Everything runs in your browser and nothing you enter is saved or sent anywhere.
Why Weeks and Months Don’t Divide Evenly
A calendar month isn’t a fixed number of weeks — it varies between roughly 4.3 weeks, depending on the month. Since pregnancy is tracked in exact weeks (40 of them, on the standard timeline), converting that into “months” always involves some rounding and approximation. That’s why you’ll see slightly different week ranges for each month depending on the source, and why some references describe pregnancy as nine months while others describe it as ten lunar months of four weeks each.
Why Providers Track Pregnancy in Weeks, Not Months
Weeks give a much more precise way to track fetal development, schedule prenatal appointments and screenings, and describe risks and milestones consistently — describing someone as “24 weeks” is far more specific than “in their sixth month,” which could mean anywhere from around week 23 to week 27 depending on the reference used. This is why your midwife or doctor will almost always refer to weeks rather than months.
Understanding the Trimester Breakdown
Alongside the month conversion, this calculator also shows which of the three trimesters a given week falls into: the first trimester spans weeks 1 to 13, the second spans weeks 14 to 27, and the third spans weeks 28 to 40. Trimesters are a more commonly referenced, broader way of describing pregnancy progress than the exact month.
Why “Weeks to 40” Is Only a General Marker
Full term is generally considered to fall between 37 and 42 weeks, and only a small share of babies actually arrive exactly at week 40 — most arrive within a week or two of that mark either way. The countdown shown here is useful for general orientation, not a prediction of exactly when labor will begin.
Frequently Asked Questions
Why do different sources give slightly different week ranges for each month?
Because calendar months aren’t a fixed number of weeks, converting exact pregnancy weeks into “months” always involves some rounding, so different references define month boundaries slightly differently.
Is pregnancy really nine months or ten months?
Both descriptions are used. “Nine months” refers to calendar months; “ten months” sometimes refers to ten four-week lunar months, since 40 weeks divides more evenly that way.
Why do providers use weeks instead of months?
Weeks are more precise for tracking development, scheduling appointments, and describing milestones consistently than the broader, less exact “month” reference.
Does this calculator store any of my information?
No. Everything runs in your browser and nothing you enter is saved or sent anywhere.
Is the “weeks to 40” countdown a due date prediction?
No. It’s a general reference against the traditional 40-week marker, not a prediction of exactly when labor will start.
You may also find our Due Date Calculator or Pregnancy Week Calculator useful.