Pregnancy weeks to months

Multiply your weeks by 7 to get days, then divide by 30.44 — the average length of a calendar month (365.25 days ÷ 12), which works out to about 4.35 weeks per month. So 22 weeks is 154 days, which is 5.1 months: you're 5 months pregnant. This tool reports completed months, because that matches how people actually say it — you're “5 months pregnant” until you finish the sixth month. Some charts disagree by one because they count the month you're currently in instead; neither is wrong, they're just different conventions applied to the same approximate math.

Because 40 weeks is 280 days, and 280 ÷ 30.44 (the average calendar month) is about 9.2 — nine months plus roughly a week. The “nine months” figure survives because it's close enough for conversation. Two other quirks feed the confusion: pregnancy is counted from the first day of your last period, about two weeks before conception, so from conception it's only about 38 weeks (8¾ months); and if you count old-fashioned four-week “lunar months,” 40 weeks is exactly 10 of them — which is where the “ten-month pregnancy” you sometimes hear comes from. Same span, different yardsticks.

Almost, but not exactly — and the gap explains a lot of chart confusion. ACOG defines trimesters in weeks and days: the first trimester runs through 13 weeks 6 days, the second from 14w0d through 27w6d, and the third from 28w0d to delivery. Three calendar months is about 13 weeks 0 days, so you complete your third month right at the start of week 13 — but the first trimester still has almost a week to run. For everyday talk the shorthand is fine; for anything clinical (screening windows, medication timing), use the week number.

Precision. Prenatal care is scheduled to windows measured in weeks and days: a dating ultrasound in the first trimester, the anatomy scan around 18–22 weeks, glucose screening at 24–28 weeks, and term starting at exactly 37 weeks 0 days. Months can't carry that precision — they vary from 28 to 31 days, and “five months pregnant” could mean anything across a three-week span depending on which convention a chart uses. Weeks from the last menstrual period are the one unambiguous clock everyone in medicine shares, which is why your provider will always want the week number, not the month.

Using the honest math (a month is about 4.35 weeks): 22 weeks is 154 days, about 5.1 calendar months — you're 5 months pregnant, mid second trimester. 28 weeks is 196 days, about 6.4 months — 6 months pregnant and the first day of your third trimester. 35 weeks is 245 days, about 8.0 months — 8 months pregnant, with roughly 5 weeks to the 40-week mark. The full chart on this page runs week by week from 1 to 42, grouped by trimester, so you can look up any week directly.

Completely. This converter runs entirely in your browser: the weeks, days, or months you enter are converted on your own device and are never sent to a server, stored, or shared — close the tab and everything is gone. In a post-Dobbs world we treat reproductive data as sensitive by default. It's an educational conversion based on ACOG's week-based conventions, not medical advice or a diagnosis — your provider dates your pregnancy in weeks and days.