Tools · Pregnancy

Pregnancy Weeks to Months Converter

How many months pregnant are you at 20, 30, or 36 weeks? Convert weeks to months and back, with the trimester and a full 40-week reference table.

How many weeks pregnant are you?

Weeks, then extra days (0–6). Your clinic writes this as 30+0.

You are in

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Calendar months

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Trimester

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Left to 40 weeks

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Enter your week to see the month and trimester.

Why the two numbers disagree

Ask how many months 30 weeks is and you will get two answers: the seventh month, and about 6.9 months. Neither is wrong. The month number comes from the standard way weeks are grouped into months of pregnancy, which is not an even four weeks each — the groups run 4, 4, 5, 4, 5, 5, 4, 4, 5 weeks to make 40. The decimal is plain calendar arithmetic: days elapsed divided by 30.44, the average length of a month.

The instinct to divide by four is where most of the confusion starts. Four weeks is 28 days; an average month is 30.44. Over a whole pregnancy that gap compounds into an extra month, which is how 40 weeks gets described as ten months. Do it the other way — 280 days divided by 30.44 — and you land on 9.2, the nine months everyone expects with a bit left over.

There is a second reason the arithmetic feels strange. Pregnancy is dated from the first day of your last period, not from conception, so the count starts roughly two weeks before there is anything to count. At 40 weeks your baby has been developing for about 38 of them. This calculator runs entirely on your device — nothing is stored or uploaded.

Every week, converted

The full mapping, with a link to what is happening each week.

Month	Weeks	Trimester	Week by week
Month 1	Weeks 1–4	First	4
Month 2	Weeks 5–8	First	5 6 7 8
Month 3	Weeks 9–13	Second	9 10 11 12 13
Month 4	Weeks 14–17	Second	14 15 16 17
Month 5	Weeks 18–22	Second	18 19 20 21 22
Month 6	Weeks 23–27	Third	23 24 25 26 27
Month 7	Weeks 28–31	Third	28 29 30 31
Month 8	Weeks 32–35	Third	32 33 34 35
Month 9	Weeks 36–40	Third	36 37 38 39 40

Frequently Asked Questions

How many months is 30 weeks pregnant?

Thirty weeks puts you in the seventh month of pregnancy, and about 6.9 calendar months along. Both numbers are correct — they answer slightly different questions. The seventh month is where week 30 falls in the standard obstetric grouping of weeks into months; 6.9 is how much calendar time has actually passed since your last period.

Why isn't a pregnancy month just four weeks?

Because a calendar month is not four weeks. The average month is 30.44 days, or about 4.35 weeks. If you divide 40 weeks by four you get ten months, which is why pregnancy is sometimes wrongly described that way. Divide the 280 days by 30.44 instead and you get about 9.2 months — the familiar nine months, plus a little.

Is 40 weeks nine months or ten months?

Nine months and roughly one week. The confusion comes from counting in four-week blocks, which produces ten. Pregnancy is dated from the first day of your last period rather than from conception, so the 40 weeks include about two weeks before conception actually happened — another reason the arithmetic feels off.

Where do the trimesters divide?

On this site the first trimester runs to the end of week 12, the second covers weeks 13 to 26, and the third starts at week 27 and runs to birth. You will see slightly different boundaries elsewhere — some sources start the third trimester at week 28 — because the divisions are conventions for discussing pregnancy rather than fixed biological events. What matters is that you use one set consistently.

My clinic counts in weeks. Should I use weeks or months?

Use weeks whenever you are talking to your care team. Every scan, test, and measurement in pregnancy is scheduled by completed weeks and days, and a month is too coarse a unit for that — the difference between 36 and 39 weeks is enormous clinically, but both are "month nine". Months are for telling family and friends where you are.