How accurate are “early detection” tests really?

Early detection tests can find smaller amounts of the pregnancy hormone hCG than standard tests, so they can sometimes show a positive before your period is due. But the claims on the box are easy to misread, and an early negative is much less reliable than one on the day your period is due.

First, what the dates on the box mean

The day your period is due is the day you’d expect your next period to start. Test makers often count your missed period as the day after that. So “up to 6 days before your missed period” means 5 days before the day your period is due.

Research doesn’t always count the same way. The study that found about 1 in 10 pregnancies hadn’t implanted by the “first day of the missed period” used that phrase to mean the day the period was expected. In this article, we use “the day your period is due” for the day you expect it.

How many pregnancies do early tests pick up?

Fewer than the headline suggests, at the very start. One brand says that in its lab testing, its most sensitive early tests picked up nearly 8 in 10 pregnancies 5 days before the period was due, and more the closer you got to your period. Test makers say their tests are over 99% accurate from the day your period is due, though that figure also comes from lab testing.

In real life, you may have ovulated later than you think, so you could be earlier in a pregnancy than the box assumes, and an early test may pick up fewer pregnancies for you than its figures suggest.

Why there may not be any hCG to find yet

Your body only starts making hCG after a fertilised egg implants, around 6 to 12 days after ovulation. It then takes a few days to build up. Ovulation usually happens 10 to 16 days before your next period, so 5 days before your period is due, some pregnancies haven’t even implanted yet. No test, however sensitive, can find hCG that isn’t there.

Our day-by-day guide from conception to a missed period shows where each step falls.

How sensitive are early tests?

Sensitivity is measured in mIU/ml, the amount of hCG a test needs to show a positive. The lower the number, the less hCG it needs. One brand’s most sensitive test is rated at 10 mIU/ml. The number, or how many days early the test can be used, is usually on the box or leaflet.

Not every test labelled “early” is equally sensitive. In a 2004 US study of 18 brands, only one could pick up 12.5 mIU/ml, about the level the researchers estimated a test needs to find 95% of pregnancies around the time a period is due. Tests have changed since then, so check the sensitivity on the box rather than relying on the word “early”.

Getting the most from an early test

Use your first pee of the day, when hCG is most concentrated.
Don’t drink lots of fluid beforehand.
Follow the leaflet exactly, and read the result within the time it gives. Ignore anything that appears later.
If it’s negative, test again on the day your period is due. If your period is late and you’re still negative, wait a few days and test again.
If you’re still getting negatives and your period hasn’t come, speak to your GP.

For timing and how to do the test, see how early can I take a pregnancy test? and the best time to take a pregnancy test.

An early positive, then a period

A positive early result is very likely to be right. But the more sensitive tests become, the more people find out about pregnancies that end very early, before or around the time a period is due. This is sometimes called a chemical pregnancy. Some people choose to wait until their period is due to test for this reason. There’s no right choice.

If you’ve had a positive test and then start bleeding, contact your maternity unit, an early pregnancy unit or NHS 111 so you can be checked, even if you think it’s a chemical pregnancy. Nobody can tell the cause of bleeding at home. Read what is a chemical pregnancy?

Early tests and fertility treatment

If you’re having fertility treatment, test on the date your clinic gives you (for IVF, this is usually around 16 days after embryo transfer). Testing earlier may give a false result. If you had a ‘trigger’ injection containing hCG, it can stay in your body for up to about 10 days and give a positive that isn’t a pregnancy. An early test won’t give you a more reliable answer than your clinic’s test date.

Questions people ask

Can an early detection test be wrong?

A positive is very likely to be right. A negative this early often isn’t the final answer, because there may not be enough hCG yet. Test again on the day your period is due.

Why is my early positive so faint?

Early on there’s only a small amount of hCG, so the line can be very light. Read what does a faint line mean?

Is it worth buying early tests?

If you want the chance of knowing a few days sooner, they can help. If an early negative would upset you or make you anxious, waiting until the day your period is due gives you a more reliable answer from a single test.

Is a digital early test as sensitive as a line test?

Not necessarily. Sensitivity depends on the test, not whether it’s digital, so check the leaflet for how many days early it can be used.

When to get help

Mild cramps that ease with rest are usually nothing to worry about. But if you’re pregnant, or think you could be, get urgent advice from your maternity unit, an early pregnancy unit or NHS 111 if you have:

any bleeding or spotting, even if it’s light
tummy pain that’s severe, on one side, or hasn’t eased after resting for 30 to 60 minutes
pain in the tip of your shoulder

Call 999 if you have bleeding along with severe tummy pain, pain in your shoulder, or feeling sick, faint or dizzy, or if the bleeding is heavy (soaking a pad soon after putting it on). Also call 999 if you have sudden, sharp and intense tummy pain and you feel very dizzy or faint, feel sick or look very pale. These can be signs of an ectopic pregnancy or a miscarriage that need treating straight away.