Lots of women find Clear Blue pregnancy tests easy to use and reliable, but if it says 1-2 weeks, it might not match how the NHS dates pregnancy. Find out why and what that means

Trying to conceive (TTC) is equally exciting and stressful as you wait for confirmation via a pregnancy test. Many women choose Clear Blue pregnancy tests , as they're over 99% accurate at detecting pregnancy and 93% accurate at telling how long you've been pregnant . Plus they're easy to use and easy to understand. However there can be a difference between how many weeks pregnant Clear Blue test results say and how the NHS dates your pregnancy. Here, we explain why and what it means.

• Click here to read our definitive guide on Days Past Ovulation (DPO), and how ovulation and conception works

One thing that has some people scratching their heads is that Clear Blue tests and the NHS work out what week your pregnancy is differently. If your Clear Blue test says that you are 1-2 weeks pregnant, the NHS would tell you that you're actually 3-4 weeks along . Whaaaat?

Why Clear Blue tests and the NHS give different due dates

If both methods are measuring pregnancy, it's natural to wonder how they can provide different results. They are both accurate. They simply use a different starting points. Clear Blue tests provide results that measure how long it has been since conception, while the NHS goes from the first day of your last period.

So how far along am I if my Clearblue test says 1-2 weeks?

It helps to understand the numbers.

The NHS determines your pregnancy from the first day of your last period .

That's because generally you'll ovulate about 14 days after your last period started. ( Try our handy ovulation calculator to work when it could happen for you .) Conception occurs 12 to 24 hours after ovulation .

And conception is the moment that Clear Blue tests start measuring from.

That means that your Clear Blue test date (depending on your menstrual cycle) measures from 2 weeks AFTER the date that the NHS uses .

So what does that mean for you? Compare your test to the chart below.

How do pregnancy tests work?

Once you become pregnant, your body starts to produce the pregnancy hormone human chorionic gonadotropin (hCG), which is what pregnancy tests are looking for.

• Head here for more information on when to take a pregnancy test.

It normally takes until around 14 days past ovulation (DPO) before it builds up enough to be detected by most pregnancy tests.

That means that generally pregnancy tests will start to pick up if you're pregnant around the first day of your missed period. That's generally 28 days after the start of your last period, depending on your cycle.

For more information and advice on using pregnancy tests, take a look at the stories linked below, or head over to our Forum to discuss your TTC journey with other parents.

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