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- A false negative pregnancy test may happen if you don't take the test first thing in the morning.
- It could also occur if you take the test fewer than 10 days after conception.
- Checking the results too soon or using an expired test could also show a false negative.
- Visit Insider's Health Reference library for more advice.
Home pregnancy tests are usually accurate, but researchers estimate that up to 5% of tests give a false negative – meaning the test says you aren't pregnant when you actually are.
There are a few reasons why you might get a false negative – you might be taking the test too early or after drinking too much water.
The best way to ensure an accurate at-home pregnancy test result is to carefully read the instructions on the box and follow them correctly.
Here are several reasons why you might get a false negative and how you can properly take a pregnancy test.
1. You took a test too early in the pregnancy
Pregnancy tests work by measuring the levels of the pregnancy hormone human chorionic gonadotropin (hCG) in your urine. The amount of hCG in your body starts to increase once a fertilized egg implants in your uterus, and can be detected about 10 days after conception.
Where you are in your cycle also matters. "Most pregnancy tests will perform well if it is at the time of your missed period, which would typically be 2 weeks after ovulation or 28 days after your last period started," says Pamela Berens, MD, an OB-GYN with UT physicians at the University of Texas.
If you take a pregnancy test before this time, you might get a negative result, even though you're actually pregnant.
2. You checked the results too soon
Your pregnancy test should come with instructions about how long you will need to wait between taking the test and checking your results - the wait time is usually about one to two minutes. This is because the antibodies in the test need time to sense the hCG in your urine and display a result.
If you check the test before the waiting time is up, you may see a negative result even if you're pregnant.
3. Your urine is too diluted
To get an accurate positive result from a pregnancy test, you need to have a high concentration of hCG in your urine, which can be affected by several factors:
- Your urine has the highest concentration of hCG levels first thing in the morning. "If you can't take a test in the morning, try to use urine that has been sitting in your bladder for around four hours.
- Drinking lots of fluids can dilute your urine and lower the concentration of hCG, so it's best to avoid drinking too much water or other drinks before taking a pregnancy test.
4. Your pregnancy test is expired or faulty
If your pregnancy test is expired, it might give a false negative result. This is because the antibodies in the test that react to hCG hormones slowly evaporate over time - eventually there will be too few antibodies to accurately sense hCG.
You should always check the expiration date on a pregnancy test before using it to make sure you're getting an accurate result - they will often expire after a year or two on the shelf.
Pregnancy tests may also be defective. However, this is more the exception than the norm since many tests come with a control indicator to prove that the pregnancy test is working properly. This indicator may show up as an additional line that appears next to the test line or a symbol that appears in a window, depending on the type of test you take.
How to properly take a pregnancy test
To get the most accurate result on a pregnancy test, it's important that you follow the instructions that come with the test. Generally, here's a round-up of what to remember before taking the test::
- Wait until at least 10 days after your last unprotected sex session to take the test.
- Take the test first thing in the morning or after holding your urine for at least four hours.
- Before starting, check the expiration date on your pregnancy test.
- Read all the instructions that come with the test to make sure you're using it correctly.
- Pee on the test stick for the recommended amount of time.
- Place the test stick down and set a timer for the number of minutes the test requires.
- When reading the test, first look for the control indicator to make sure the test is working.
- Read the test, carefully following the instructions for how to interpret it.
- If the test results are unclear, wait a day before trying again with another test, or reach out to your doctor for a follow-up.
Next steps
If you aren't pregnant, your period should usually come about 28 days after your last period started. If your period is late, it may be a sign that you're pregnant, but there are many other reasons for a late period.
"If [a late period] is unusual for you, then you should probably see a doctor," Berens says, adding that weight changes, thyroid disease, and hormone imbalances can also be to blame for an irregular period.
Your doctor can also conduct a pregnancy blood test, which is more sensitive to hCG and can double-check your urine test result.
Insider's takeaway
Getting a false negative on a pregnancy test is relatively rare, but it is possible, particularly if you take a test soon after ovulation. To reduce your risk of a false negative, take the test first thing in the morning and follow test instructions carefully.
False negatives are usually caused by testing errors, and medications like birth control or antibiotics shouldn't make any difference.
However, certain fertility drugs like Novarel and Pregnyl contain hCG, which can lead to a false positive result, where the test says you're pregnant when you really aren't.