Pregnancy Weeks to Months Calculator
Convert weeks pregnant into months — by the calendar, by the common month-of-pregnancy chart and in four-week months — or months back into weeks, with your trimester, time to 40 weeks and a full week-by-week chart.
How it works
total days = weeks × 7 + extra days · calendar months = total days ÷ 30.44 (365.25 ÷ 12) · four-week months = total days ÷ 28 · months → weeks: months × 30.44 ÷ 7 · month of pregnancy from the common chart (month 1 = weeks 0–4 … month 9 = weeks 36–40)
Pregnancy is measured in weeks, but people often want a month figure — and there are three ways to give one. Calendar months: the average month is about 30.44 days (roughly 4.35 weeks), so dividing the total days by 30.44 gives the true calendar figure and 40 weeks lands near 9.2 months. Four-week months: dividing by 28 days makes 40 weeks exactly 10 “months”, which is why some sources talk about ten lunar months. The common month-of-pregnancy chart used by many pregnancy guides splits the 40 weeks into nine months of four or five weeks (month 3 ends at 13 weeks, month 6 covers weeks 23–27, month 9 is weeks 36–40). The calculator shows all three, plus the trimester (second from 14 weeks, third from 28) and the time left to 40 weeks, and it can also convert a number of months back into weeks.
Worked example
24 weeks and 0 days is 168 days. Divided by 30.44 that is 5.5 calendar months — five months and about two weeks — while the common chart puts week 24 in month 6, and in four-week months it is exactly 6.0. It is the second trimester, with 16 weeks left until 40 weeks. Going the other way, 6 calendar months is about 183 days, or 26 weeks 1 day.
Frequently asked questions
Why isn’t one month just four weeks?
Four weeks is 28 days, but the average calendar month is about 30.44 days. Using four weeks would make 40 weeks look like 10 months, when a full-term pregnancy is really about nine calendar months. Both figures are shown so you can compare.
How many months is 40 weeks?
About 9.2 calendar months (280 ÷ 30.44), or 10 four-week months. That is why full term is described as roughly nine months even though it spans 40 weeks.
Is 24 weeks five or six months pregnant?
Both answers are used. By the calendar, 24 weeks is about five and a half months completed; by the common pregnancy chart it is month 6 (weeks 23–27), the month you are in. The calculator shows both.
Which trimester am I in?
The common split is first trimester up to 13 weeks 6 days, second from 14 to 27 weeks 6 days, and third from 28 weeks to birth.
Related calculators
Educational estimate — clinicians track pregnancy in weeks; month figures are approximate.