How many months is 12 weeks pregnant?

Twelve weeks is the end of month 3 and the end of the first trimester. Month 3 runs from week 9 to week 13, so at 12 weeks you are in the fourth week of month 3 with one week of the first trimester left.

How many months is 20 weeks pregnant?

Twenty weeks is month 5, and it is the halfway point of a 40-week pregnancy. Month 5 covers weeks 18 to 22, so week 20 sits in the middle of it, in the second trimester.

How many months is 24 weeks pregnant?

Twenty-four weeks is month 6, in the second trimester. Month 6 runs from week 23 to week 27, so at 24 weeks you have just started it.

How many months is 16 weeks pregnant?

Sixteen weeks is month 4, the first month of the second trimester. Month 4 covers weeks 14 to 17, so week 16 is the third week of it.

How many months is 18 weeks pregnant?

Eighteen weeks is the start of month 5, in the second trimester. Month 4 ends at week 17, so week 18 begins the next month.

Why is it not just weeks divided by four?

Four weeks is 28 days and most calendar months are 30 or 31, so dividing by four drifts further out the further along you are. Dividing 40 weeks by four gives ten months, which is why the maths feels wrong. Obstetric months are defined by week ranges instead, which is what clinicians and the NHS use.

How many weeks is 6 months pregnant?

Six months covers weeks 23 to 27. So the answer people usually want is that you reach six months at week 23 and finish it at the end of week 27.

How many months is 40 weeks?

Forty weeks is the end of month 9, which is full term. Pregnancy is often described as nine months even though 40 weeks is closer to nine and a bit calendar months, and that gap is exactly the confusion this page exists for.

Pregnancy weeks to months: how many months am I?

Pregnancy weeks to months

Pregnancy week

Worked out in your browser. Nothing you enter is sent anywhere.

Why the maths feels wrong

Forty weeks divided by four is ten, and nobody says they were pregnant for ten months. The gap is that four weeks is 28 days while a calendar month is 30 or 31, so a "month" of pregnancy and a month on the wall are different lengths, and the error compounds the further along you get.

Clinicians get around this by not dividing at all. Pregnancy months are defined as ranges of weeks, four or five weeks each, adding to 40. That is the mapping below, and it is the one your midwife is using.

Pregnancy months by week

Month	Weeks	Trimester
Month 1	Weeks 1–4	First
Month 2	Weeks 5–8	First
Month 3	Weeks 9–13	First
Month 4	Weeks 14–17	Second
Month 5	Weeks 18–22	Second
Month 6	Weeks 23–27	Second
Month 7	Weeks 28–31	Third
Month 8	Weeks 32–35	Third
Month 9	Weeks 36–40	Third

Every week, converted

Week	Month	Trimester	Days
4 weeks	Month 1	First	28 days
5 weeks	Month 2	First	35 days
6 weeks	Month 2	First	42 days
7 weeks	Month 2	First	49 days
8 weeks	Month 2	First	56 days
9 weeks	Month 3	First	63 days
10 weeks	Month 3	First	70 days
11 weeks	Month 3	First	77 days
12 weeks	Month 3	First	84 days
13 weeks	Month 3	First	91 days
14 weeks	Month 4	Second	98 days
15 weeks	Month 4	Second	105 days
16 weeks	Month 4	Second	112 days
17 weeks	Month 4	Second	119 days
18 weeks	Month 5	Second	126 days
19 weeks	Month 5	Second	133 days
20 weeks	Month 5	Second	140 days
21 weeks	Month 5	Second	147 days
22 weeks	Month 5	Second	154 days
23 weeks	Month 6	Second	161 days
24 weeks	Month 6	Second	168 days
25 weeks	Month 6	Second	175 days
26 weeks	Month 6	Second	182 days
27 weeks	Month 6	Second	189 days
28 weeks	Month 7	Third	196 days
29 weeks	Month 7	Third	203 days
30 weeks	Month 7	Third	210 days
31 weeks	Month 7	Third	217 days
32 weeks	Month 8	Third	224 days
33 weeks	Month 8	Third	231 days
34 weeks	Month 8	Third	238 days
35 weeks	Month 8	Third	245 days
36 weeks	Month 9	Third	252 days
37 weeks	Month 9	Third	259 days
38 weeks	Month 9	Third	266 days
39 weeks	Month 9	Third	273 days
40 weeks	Month 9	Third	280 days

What this changes if you are expecting twins

The conversion is the same, but the finish line usually is not. Twins are commonly born around 36 to 37 weeks rather than 40, so a twin pregnancy often ends partway through month 9 or at the start of it. If you are counting down in months, count to eight and treat the ninth as a bonus.

That also moves everything that is supposed to happen "in the last month". Hospital bag, car seats, the name argument: bring them all forward by about a month if you are carrying more than one.

Where the app fits

Once they are here the counting changes from weeks pregnant to weeks old, and with two babies it becomes two sets of numbers. Multibaby keeps each baby's age, feeds, sleep and growth on its own track, so you are not doing that arithmetic in your head at 3am. The baby age converter does the same weeks-to-months job for after the birth.

Quick answer

Pregnancy months do not line up with calendar months, which is why dividing weeks by four gives the wrong answer. Pregnancy is counted as 40 weeks split into nine obstetric months of four to five weeks each: 12 weeks is month 3, 16 weeks is month 4, 20 weeks is month 5, 24 weeks is month 6, and 32 weeks is month 8. Enter any week below to see its month, its trimester and how many days that is.

How to use it

Enter your current week. Type the pregnancy week you are in, from 1 to 42. If you are not sure, work it out from your due date with the pregnancy week calculator first.
Read the month and trimester. You get the obstetric month that week falls in, which week of that month it is, and which trimester.
Check the table for any other week. The full week-by-week table below covers weeks 4 to 40, so you can look up any week without re-entering it.

Frequently asked questions

How many months is 12 weeks pregnant?: Twelve weeks is the end of month 3 and the end of the first trimester. Month 3 runs from week 9 to week 13, so at 12 weeks you are in the fourth week of month 3 with one week of the first trimester left.
How many months is 20 weeks pregnant?: Twenty weeks is month 5, and it is the halfway point of a 40-week pregnancy. Month 5 covers weeks 18 to 22, so week 20 sits in the middle of it, in the second trimester.
How many months is 24 weeks pregnant?: Twenty-four weeks is month 6, in the second trimester. Month 6 runs from week 23 to week 27, so at 24 weeks you have just started it.
How many months is 16 weeks pregnant?: Sixteen weeks is month 4, the first month of the second trimester. Month 4 covers weeks 14 to 17, so week 16 is the third week of it.
How many months is 18 weeks pregnant?: Eighteen weeks is the start of month 5, in the second trimester. Month 4 ends at week 17, so week 18 begins the next month.
Why is it not just weeks divided by four?: Four weeks is 28 days and most calendar months are 30 or 31, so dividing by four drifts further out the further along you are. Dividing 40 weeks by four gives ten months, which is why the maths feels wrong. Obstetric months are defined by week ranges instead, which is what clinicians and the NHS use.
How many weeks is 6 months pregnant?: Six months covers weeks 23 to 27. So the answer people usually want is that you reach six months at week 23 and finish it at the end of week 27.
How many months is 40 weeks?: Forty weeks is the end of month 9, which is full term. Pregnancy is often described as nine months even though 40 weeks is closer to nine and a bit calendar months, and that gap is exactly the confusion this page exists for.