Clearblue tests are easy to use, accurate, and can even tell you how long you've been pregnant, but how does that date compare with what the NHS says?

When it comes to pregnancy tests, Clearblue make some of the most popular tests in the UK. They're accurate ( 99% for pregnancy, 93% for the date ), easy to use and some even give you a date for roughly how long you've been pregnant. However for many women, those dates can be a little confusing as what their Clearblue test gives them is different to what the NHS says about the stage of pregnancy.

Trying to conceive (TTC) is a wonderful but stressful time.

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

Why do pregnancy tests give different dates from the NHS?

If both Clearblue tests and the NHS measure pregnancy, it's natural to wonder how they can provide different results. They are both accurate. They simply use a different starting points.

The NHS dates your pregnancy from the first day of your last period . In contrast, Clearblue pregnancy tests go from the date of conception .

If you have an average 28-day menstrual cycle, then the date of conception is usually around 14 days after your period started .

( Try our handy ovulation calculator to work when it could happen for you .)

Explaining the timings

OK, get ready for some dates.

You period starts - This is when the NHS would measure from.

Around 14 days later, on average - You'll probably ovulate, if you have an average 28-day cycle. (You can try our handy ovulation calculator to work out when it could happen for you .)

Conception - Typically happens 12 to 24 hours after ovulation. This is when Clearblue will measure from.

So your Clearblue test date is taken from around 2 weeks after the date the NHS uses (depending on the length of your menstrual cycle, of course).

So how far along am I if my Clearblue test says 3+ weeks?

That means that if your Clearblue test is saying 3+ weeks, then the NHS would say that you are 5 or more weeks pregnant .

ompare your test to the list below:

• If your Clearblue test says 1-2 weeks, that's 3-4 weeks according to the NHS .
• If your Clearblue test says 2-3 weeks, that's 4-5 weeks according to the NHS .
• If your Clearblue test says 3+ weeks, that's 5+ weeks according to the NHS .

However, you will need to adjust this slightly if you have particularly long or short cycles.

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.

• When should I 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.

If you'd like to learn more about pregnancy tests and the TTC journey, take a look at the stories linked below. If you've got any questions you want to ask of people who've been through what you're going through, head on over to the Forum.

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