How Many Weeks Pregnant Calculator

"How far along are you?" is a question you'll hear a lot once you're pregnant, and the answer isn't always obvious. Pregnancy is counted in a way that can feel back to front, and apps, scans and midwives don't always phrase it the same way.

Our How Many Weeks Pregnant Calculator gives you the exact answer in weeks and days. If you want the full picture, including your due date and scan dates, our main Pregnancy Calculator covers everything in one place.

How weeks of pregnancy are counted

In the UK, pregnancy is counted from the first day of your last period, not from the day you conceived. Conception usually happens about two weeks later, around ovulation. So by the time you conceive, you're already counted as about 2 weeks pregnant.

This sounds odd, but it's done for a good reason: most people know when their last period started, while very few know exactly when they conceived. Counting from the same starting point means every pregnancy is dated in the same way.

A full-term pregnancy lasts around 40 weeks from the first day of your last period, which is 280 days.

How to use the calculator (How Many Weeks Pregnant Calculator)

1. Choose what to calculate from: your last period, your due date or the date you conceived.
2. Enter the date.
3. If you're using your last period, enter your average cycle length. The calculator adjusts for cycles longer or shorter than 28 days.

You'll see how many weeks and days pregnant you are today, which week of pregnancy you're in, your trimester, your due date and how far through your pregnancy you are.

Weeks pregnant vs which week you're in

These two ways of describing your pregnancy are easy to mix up:

• 10 weeks and 3 days pregnant means 10 full weeks have passed.
• That means you're in your 11th week of pregnancy.

Some apps say "week 11" when your midwife says "10 weeks". Both are right, they're just counting in different ways. The calculator shows both.

Using your due date instead

If you've had your dating scan, use the due date from your scan. It's usually more accurate than a date based on your period, because the scan measures your baby's size. Your midwife will use the scan date for the rest of your care, so it makes sense to count from it too.

If you know your exact conception date, for example from ovulation tests, the calculator counts back 2 weeks to the equivalent last period date. For pregnancies after fertility treatment, our IVF Due Date Calculator uses your transfer date instead.

A worked example

With the calculator's default settings, you'll see an example of someone 12 weeks pregnant:

• 12 full weeks since the first day of their last period
• They're in week 13, the last week of the first trimester
• Their due date is 28 weeks away

Enter your own date to see your figures.

Key weeks in pregnancy

• Around 8 to 12 weeks: your booking appointment with a midwife.
• 10 to 14 weeks: your dating scan, sometimes called the 12-week scan.
• 14 weeks: the second trimester starts. Our Pregnancy Trimester Calculator shows the exact dates for you.
• 18 to 21 weeks: your anomaly scan, often called the 20-week scan.
• 28 weeks: the third trimester starts.
• 37 weeks: your baby is considered full term.
• 40 weeks: your due date. Count down to it with our Pregnancy Countdown Calculator.