How Many Weeks Pregnant Am I?

So you’ve just found out that you’re pregnant! One of the first things you may be wondering is: how many weeks pregnant am I?!

An important thing to realise is that when doctors or midwives calculate your estimated due date, it’s using a formula based on averages which wont be totally accurate. It’ll give you a fairly good estimate of when you’ll be due, but don’t rely too heavily on the date though. As little as 3-5% of babies are born on their due date.

A full term pregnancy is 38 to 42 completed weeks of pregnancy. The estimated due date (or as I like to call it the ‘guess date’) is right in the middle of those weeks – 40 weeks. So if you prepare for the likelihood of 42 weeks of pregnancy, you’ll experience less disappointment if your estimated date comes and goes. First pregnancies tend to last longer than subsequent too.

Many factors come into play, so you can never be completely accurate as to a baby’s due date! A study was even published where they recorded guesses from doctors, midwives and mothers – and no-one was more accurate than the other!

How Many Weeks Pregnant Am I?

Week 1 of your pregnancy starts on the first day of your last period. Weird huh?! But it’s an exact date doctors and midwives can go by. Unless you’ve had assisted conception and know exactly when the egg was fertilised, the exact moment of ovulation and conception is usually unknown. The reason why due dates are so inaccurate is that it’s assumed you have a 28 day menstrual cycle with ovulation on day 14. As you may know, every woman has a unique cycle length and phases. You may have a shorter or longer cycle than 28 days and you may have ovulated any time in between! But for the sake of a date, everyone’s pregnancy is calculated based on an average. Therefore when you miss your first period, you’re already 4 weeks pregnant.

To find out how many weeks pregnant you are, use our pregnancy calculator which will give you an estimated due date and estimated date of conception. It will also tell you how many weeks pregnant you are and how long you have to go until you reach the end of full term pregnancy at 42 weeks.

What If I Don’t Know When My Last Period Was?

If you don’t remember when your last period was or if you’ve not had a period for a while, you can book an early pregnancy ultrasound to try and work out how many weeks pregnant you are. Calculations based on your own, unique cycle is most accurate, followed by early ultrasound, then late ultrasound. The reason for this is that when a baby first forms, they follow some pretty uniform growth pattern as they develop all the necessary building blocks. But as they get bigger, they develop at their own rate – genetics come into play!

Its best to avoid ultrasounds where you can, especially early ultrasounds which are usually internal. This means the ultrasound is placed very close to your developing baby. Have an ultrasound if you must, but try to keep the time to a minimum and avoid any that are unnecessary.

What Happens During Each Week Of Pregnancy?

Don’t forget to visit our pregnancy week by week section, which contains information about changes in your body and your baby, week by week. Each week also has an image of what your baby and belly might look like! All the best for a wonderful pregnancy.

Last Updated: April 19, 2015


Kelly Winder is the creator of, a doula, writer and mother to three awesome children. Currently, she's travelling the world for 12 months with her partner and children, and hopes to inspire more families to do the same. Visit for more information.

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