How Do I Calculate My Pregnancy Week by Week?

Knowing how many weeks along you is essential during pregnancy. It will ensure that you’re getting the right antenatal care and that your ultrasound scans are scheduled at the appropriate time. You will also be able to check our pregnancy week by week guide to find out what to expect at this stage in your pregnancy. Pregnancy is a long journey that will involve many different changes to your body, so it is important to learn what you can expect from the coming weeks and months.

How Do I Calculate My Pregnancy Week by Week?

Dating Your Pregnancy

Working out the length of your pregnancy is one of the first things you should do after you take a positive pregnancy test. Most doctors and pregnancy week by week guides will date your pregnancy from the start of your last period. If you’ve been monitoring your cycle while trying for a baby or you keep a record of your periods, then this will be easy. However, if you’re not sure when you had your last period, you might still be able to estimate the date.

The first day of the last period you had before you became pregnant is counted as the first day of the pregnancy. When people talk about how many weeks pregnant you are or you look at a pregnancy week by week guide, this is the date you should count from too. We’ve provided a pregnancy calculator on our site to help you to do this.

Although this is the most common method for dating a pregnancy, it isn’t based on when you conceived. Conception happens when you are ovulating, not during your period. For an average menstrual cycle, this happens a couple of weeks after your period. We count the weeks of your pregnancy from your last period because it is more convenient (you’re more likely to know when your period was than when you ovulated), but this means that you aren’t pregnant for the first couple of weeks.

Getting a More Accurate Date

Dating your pregnancy by your last period is a simple way to estimate how far along you are, but it isn’t always accurate because:

  • You might not know exactly when your last period started
  • Women can have cycles of different lengths, which means that the time between your period and ovulation can vary
  • Some women experience spotting or bleeding in early pregnancy, which can sometimes be mistaken for a period, so you might be dating your pregnancy from the wrong point

However, this doesn’t mean that it’s impossible to work out exactly how pregnant you are. You’ll get the most accurate date for your pregnancy when you have your first ultrasound scan. By checking your baby’s development and measuring him or her, we can work out how far along you are. We’ll tell you how many weeks pregnant you are so that you’ll be able to check our pregnancy week by week guide and plan ahead for your pregnancy.

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137 Harley Street,
London W1G 6BF

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Baker Street
Regent’s Park
Great Portland Street

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Alderley Edge Medical Centre, Talbot Road, Alderley Edge,
Cheshire, SK9 7HR

Nearest Overground Train Station Alderley Edge

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Harley Street, London

The Birth Company
137 Harley Street

020 7725 0528

Harley Street, London Opening Times

Mon 08:00 - 20:00
Tue 08:00 - 20:00
Wed 08:00 - 20:00
Thu 08:00 - 20:00
Fri 08:00 - 18:00
Sat 09:00 - 16:00
Sun 10:00 - 14:00

Alderley Edge, Cheshire

The Birth Company
Alderley Edge Medical Centre,
Talbot Road,
Alderley Edge

016 2570 4080

Alderley Edge, Cheshire Opening Times

Mon 09:00 - 17:00
Tue 09:00 - 17:00
Wed 09:00 - 17:00
Thu 09:00 - 17:00
Fri 09:00 - 17:00
Sat Closed
Sun Closed
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