Pregnancy math may rapidly become perplexing. Is it week 12 or 13 for you? Is it your first or second trimester? Is it better to be three or four months pregnant?

Fortunately, once you know what to count, the solutions are (relatively) straightforward. Here's all you need to know about pregnancy's weeks, months, and trimesters, as well as where you fit in.

How many weeks are in a pregnancy?

A pregnancy lasts 40 weeks (or 280 days). The first day of your last menstrual cycle is used to calculate your due date (even though most pregnancies are not conceived until two weeks later). It's important to remember that only approximately 30% of pregnancies make it to week 40.

How many weeks are in a trimester?

Each trimester lasts 13 or 14 weeks (simply divide 40 by three to understand why the breakdown isn't accurate).

How many trimesters are in a pregnancy?

A pregnancy is divided into three trimesters: the first trimester, which lasts about weeks 1 to 13, the second trimester, which lasts generally weeks 14 to 27, and the third trimester, which lasts approximately weeks 28 to 40. (and up).

Is pregnancy nine or 10 months long?

Your pregnancy is counted as nine months if you are 40 weeks pregnant. But wait... there are four weeks in a month, thus 40 weeks equals ten months. Right? No, not at all. Four weeks equals 28 days, but months have 30 or 31 days (with the exception of February, of course), making each month around 4.3 weeks long.

How many weeks is a full-term pregnancy?

A full-term pregnancy lasts from the beginning of 39 weeks to the conclusion of 40 weeks if you're carrying a single child. A full-term pregnancy is defined as at least 38 weeks if you're carrying twins.

Depending on when your baby is delivered, the American College of Obstetricians and Gynecologists (ACOG) has defined the following terminologies during pregnancy:

20 weeks to 37 weeks is considered preterm.
37 weeks 0 days to 38 weeks 6 days (early term)
39 weeks 0 days to 40 weeks 6 days (full term)
41 weeks 0 days to 41 weeks 6 days (late term)
After 42 weeks and 0 days, the term ends.

Pregnancy months to weeks chart

If these explanations are making your head spin, here's a quick rundown of how the weeks, months, and trimesters are roughly measured in pregnancy:

Trimester 1

Month 1: Weeks 1 to 4
Month 2: Weeks 5 to 8
Month 3: Weeks 9 to 13

Trimester 2

Month 4: Weeks 14 to 17
Month 5: Weeks 18 to 22
Month 6: Weeks 23 to 27

Trimester 3

Month 7: Weeks 28 to 31
Month 8: Weeks 32 to 35
Month 9: Weeks 36 to 40

How do I know what week I am currently in my pregnancy?

You're 15 weeks pregnant, according to your doctor, but you're also informed you're in week 16. Which is the correct answer? The short answer is yes. Your due date is the same in both circumstances; the terminology used to allude to it differs.

It turns out that the number of weeks you've been pregnant differs from the number of weeks you've been pregnant. You're 15 weeks and some days pregnant if you're at week 16. Because you are both 15 weeks pregnant and in week 16 of pregnancy, people think you are both 15 weeks pregnant and in week 16 of pregnancy.

Consider birthdays to help you sort things out. You weren't even a day old when you were born, yet you were in your first week of existence. You had completed your first year and were beginning your second when you became one year old. On other words, you were in the first day of your second year on your first birthday. However, no one told you that you were two years old until you had completed your second year and had began your third.

When discussing your weeks of pregnancy, the same criteria apply: You are x weeks pregnant, but in your x+1 week of pregnancy.

How do I calculate my due date?

Have you checked in with your doctor about your expected due date yet? Instead of calculating from the day you conceived, it's measured from the first day of your last menstrual period (LMP). So try to recall the first day of your LMP and multiply it by 40 weeks.

If you're good with numbers, you may use the following method to figure out your due date:

Subtract three months from your LMP's start date.
Seven days are added.
1 year is added
Subtract three months from the start date of your LMP, for example, to get 3/2/2020. 3/9/2020 is the result of adding seven days. Finally, add a year to get your projected due date of March 9, 2021.

Why is pregnancy calculated from your last period?

Why start the clock on pregnancy before sperm meets egg (and, in fact, before your ovary ever releases the fated egg that will give birth to your child)? Simply said, the LMP is a more accurate day to date a pregnancy from. Even if you're a master of cervical mucus and know exactly when you ovulated and when you had intercourse, you're unlikely to be able to identify the precise moment of conception.

Because sperm may linger out and wait for an egg to fertilise for three to five days after they arrive, and an egg can be fertilised for up to 24 hours after it's been released, there's a broader window than you might expect. That's also wonderful news, since it means you'll have been pregnant for four weeks by the time you miss your period.

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#40weeks