How Many Weeks Pregnant Am I?

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 due date, they use a method as a fairly good estimate of when you’ll be due – don’t rely too heavily on this date though as only as little as 5% of babies are born on their due date. A full term pregnancy is 38 to 42 completed weeks of pregnancy, with the estimated due date (I like to call it the ‘guess date’!) 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. So many factors come into play that you can never be accurate as to a baby’s due date – and a study was even done where they got guesses from doctors, midwives and mothers – and no-one was more accurate than the other!

Understanding Weeks of Pregnancy

Week 1 of your pregnancy starts on the first day of your last period. Weird huh?! But its an exact date doctors and midwives can work by – unless you’ve had assisted conception and know exactly when the egg was fertilised, the exact moment of ovulation is usually unknown. And here comes another calculation which is flawed – it is assumed you have a 28 day 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, you are classed at an ‘average’. Therefore when you miss your first period, you’re already 4 weeks pregnant.

Bearing in mind that no due date is completely accurate, to find out how many weeks pregnant you are, use our pregnancy calculator which will give you an estimated due date, estimated date of conception, how many weeks pregnant you are and how long 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 due to medications or were breastfeeding etc., you can get an early pregnancy ultrasound to try and work out how many weeks pregnant you are. Working it out based on your cycle is most accurate, followed by early ultrasound, then later ultrasound. The reason for this is that when a baby first forms, they follow some pretty uniform growth pattern as they develop. But as they get bigger, they develop at their own rate – genes 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 In Each Week Of Pregnancy?

Don’t forget to check out 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!

Last Updated: February 23, 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.

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