False negative pregnancy test: why it happens and when to test again

Yes, a negative pregnancy test can be wrong. A positive test is almost certainly right, but a negative one is less reliable. If your period still hasn’t come, you could still be pregnant.

How often does it happen?

More often than people expect, especially if you test early. The US Food and Drug Administration (FDA) says 10 to 20 in every 100 pregnant women won’t get a positive result around the day their period is due. Early tests used before then miss more. That isn’t because the tests are faulty. It’s usually because there isn’t enough of the pregnancy hormone hCG yet.

Why a test might say negative when you’re pregnant

You tested too early

The most common reason. hCG only starts to build up after the fertilised egg implants, around 6 to 12 days after ovulation, and then takes a few days to reach a level a test can find.

You ovulated later than you thought

Ovulation usually happens 10 to 16 days before your next period, not on a fixed day. If you ovulated late, you’re less far along than you think, and so is your hCG. For example, if you usually have 28-day cycles but ovulated around day 20 this month, on day 29 you’d only be about 9 days past ovulation. That’s too early for many pregnancies to show on a test.

Your cycle is irregular

If you don’t know when your period is due, it’s easy to test too early. The NHS says to test at least 21 days after you last had unprotected sex.

Your pee was diluted

Drinking a lot before testing can make a small amount of hCG harder to find. If you’re testing early, use your first pee of the day, when it’s most concentrated.

The test wasn’t done or read as the leaflet says

For example, not enough pee on the stick, or reading the result before the time it says.

The test isn’t sensitive enough for how early you are

Tests vary in how little hCG they can pick up, measured in mIU/ml. The most sensitive early tests are rated at around 10 mIU/ml. Check the box, and the expiry date. Read hCG levels and pregnancy test sensitivity.

Very rarely, too much hCG

Very high hCG levels can stop a urine test working properly, so it shows negative. This is called the hook effect. It happens because the test’s chemistry gets overwhelmed and can’t form a line. It’s rare.

Can I still be pregnant if I tested negative?

If you tested before or on the day your period was due, yes, it’s possible. hCG rises quickly in early pregnancy, so if your period still hasn’t arrived, test again in a few days.

If you’ve had two negative tests a few days apart and your period still hasn’t come, speak to your GP. Periods can be late for lots of reasons other than pregnancy: see pregnancy or a late period? and, if you have symptoms, feeling pregnant but testing negative.

Ectopic pregnancy and negative tests

An ectopic pregnancy, where a pregnancy grows outside the womb, usually gives a positive test. But the NHS says to get medical advice if you have symptoms of one and you might be pregnant, even if you haven’t had a positive test. Symptoms usually start between 4 and 12 weeks of pregnancy and can include:

tummy pain low down on one side
vaginal bleeding or a brown watery discharge
pain in the tip of your shoulder
discomfort when peeing or pooing

When to test again

Wait a few days, then test again with your first pee of the day. If your period is overdue, one brand suggests testing again 3 days later.
Follow the instructions carefully and read the result within the time it says.
If your second test is negative and your period still hasn’t come, speak to your GP. They can talk through other reasons and may suggest tests.
In the meantime, it’s sensible to carry on as if you could be pregnant: keep taking folic acid, and avoid alcohol and smoking.

If you’re having 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. Don’t stop any medicines your clinic has prescribed unless they tell you to. If you have any bleeding or a brown, watery discharge, contact your fertility clinic or NHS 111 as soon as possible.

Questions people ask

How long should I wait before testing again?

A few days. hCG rises quickly in early pregnancy, so a few days can make a difference. If it’s still negative and your period hasn’t come, see your GP.

Can you be pregnant for weeks and still test negative?

It’s uncommon once your period is more than a few days late, but it can happen if you ovulated much later than usual. Very rarely, very high hCG can stop a test working. If you keep getting negatives and your period hasn’t come, see your GP.

Does drinking water affect a pregnancy test?

It can early on, because it dilutes your pee. From the day your period is due there’s usually enough hCG for this not to matter.

Would a blood test show something a home test doesn’t?

A blood test measures exactly how much hCG there is, rather than just saying yes or no. You won’t usually need one, but your GP or an early pregnancy unit may arrange one if things are unclear.

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.