Pregnancy weeks to months: How far along are you?

Pregnancy is measured in weeks by the health professionals who care for us. But you might have noticed that other people often ask, “How many months along are you?” — and figuring out the answer can sometimes be confusing. But with our simple pregnancy weeks-to-months calculator, you can easily translate your weeks of pregnancy into months. Plus, you can learn how weeks and months in pregnancy are calculated, how trimesters fit in, and why these tracking methods are helpful.

How do you calculate weeks into months in pregnancy? 

When doctors calculate where you are in your pregnancy, they typically count starting from the first day of your last menstrual period (LMP). Confusingly, that means that in the first two weeks or so of pregnancy — from the start of your previous period up until ovulation and conception — you’re not actually pregnant yet.

Your due date is usually calculated by counting 40 weeks (or 280 days) from the day of your LMP. Flo’s pregnancy due date calculator can show you your estimated due date (EDD) if you’re keen to know before your doctor confirms it. Remember that your EDD is never a guaranteed birth date, but it’s important because it’s used as a measure of your baby’s growth throughout pregnancy.

“Pregnancy usually lasts 40 to 41 weeks. But your due date is the 40-week mark,” says obstetrician and gynecologist Dr. Charlsie Celestine, New Jersey, US. “Most doctors prefer to think and discuss in weeks.” That’s because it allows them to measure the baby’s development more carefully.

So, if you’re asked how many months pregnant you are by friends and family, how do you answer? Converting pregnancy weeks into months can be tricky because months aren’t a clean-cut four weeks. In fact, a month averages a little over four weeks. But Flo’s calculator can help you convert pregnancy weeks into months. 

We’ve also created a pregnancy weeks to months chart so you can see how it all stacks up. But remember that this isn’t an exact science because doctors never count pregnancy in months, and some months are longer or shorter than others:

As you move through the weeks, months, and trimesters of pregnancy, it can be helpful to use a pregnancy-tracking app like Flo to stay connected to your baby’s growth. You can track the milestones as they happen, get extra guidance along the way, and, if you’d like to, you can share it all with your partner.

How many weeks are in a pregnancy?

A full-term pregnancy typically lasts for 40 weeks, starting from the date of your last menstrual period. “Most people don’t get a positive pregnancy test until they are already about four weeks pregnant. This is a result of the way we calculate the due date,” explains Dr. Celestine.

Every pregnancy is different, and it doesn’t always last the expected amount of time. Here’s how it’s categorized based on when in the pregnancy a baby is born:

Preterm: any time before 37 weeks

Early term: 37 weeks to 38 weeks 6 days

Full term: 39 weeks to 40 weeks 6 days

Late term: 41 weeks to 41 weeks 6 days

Post term: 42 weeks and after

How many weeks are in a trimester?

Pregnancy is divided into three stages called trimesters. Each trimester is approximately 12 to 13 weeks long (although your 3rd trimester may be shorter than that, depending on when you give birth) and marks an important phase of development for both you and your baby. It’s important to know what trimester you’re in, says Dr. Celestine, because “there are certain milestones in each trimester for fetal development and certain tests like blood work that need to be completed at certain specific times in your pregnancy.”

Here’s a quick rundown of what happens in each trimester

1st Trimester: Weeks 1 to 13 (Months 1 to 3)

During the 1st trimester, your fertilized egg changes from a small group of cells to a fetus with human features. The 1st trimester can be an exciting time, but many people also experience symptoms like pregnancy sickness and fatigue as they adjust to new pregnancy hormone levels.

2nd Trimester: Weeks 14 to 27 (Months 4 to 6)

The 2nd trimester can feel more enjoyable for some people than the 1st, as symptoms like pregnancy sickness are usually less of an issue, and energy levels can feel higher. The risk of miscarriage is also much lower after the 1st trimester, which can calm feelings of anxiety. During this time, you might also start to feel your baby move, which may make it all feel more real. And, if you want to, you can usually find out the sex of your baby at around 20 weeks.

3rd Trimester: Weeks 28 to 40 (Months 7 to 9)

Your baby will continue to grow and prepare for living outside of your body during the 3rd trimester. Meanwhile, your body is hard at work putting the finishing touches on your baby and getting it ready to meet the world. 

So, when is your due date?

Your due date is an estimate of when you might meet your baby for the first time. However, only about 1 in 20 babies are born on their due date. Most arrive within a couple of weeks on either side, so it can help to build this into your expectations. 

As we know, due dates are calculated from the date of your last menstrual period. If you have irregular periods — or don’t remember your LMP — it might be a little trickier to figure out your due date this way. But doctors will always use an early ultrasound to confirm their prediction anyway, so you will always end up with an estimated due date.

Using a pregnancy-tracking app like Flo can help you keep up with your baby’s development and what to expect at every stage. “I love pregnancy tracker apps,” says Dr. Celestine. “Not only are they fun, but they’re usually pretty good at keeping you informed about what’s happening as the pregnancy progresses.”