HIV Testing: Window Periods, Results and Home Kits
Quick answer
No HIV test works immediately. The CDC says a NAT can usually detect HIV 10 to 33 days after exposure, a lab antigen/antibody test 18 to 45 days, a finger-prick antigen/antibody test 18 to 90 days, and an antibody test, which includes home self-tests, 23 to 90 days. If you test negative before your test's window has passed, test again after it. If the exposure was in the last 72 hours, ask about PEP instead of waiting.
Which of these fits you?
Tick the field marks that match.
If the first item fits, go for care and ask about PEP before testing. This is not a diagnosis. Check the window period for the test you choose so the timing fits.
If you are searching for this, you are probably waiting for an answer and want to know whether a test result can be trusted. The short version is that the right test depends on how long ago the possible exposure was. This page explains the window periods, how to read results, and where home kits fit.
What is the window period for an HIV test?
The window period is the time between exposure to HIV and the point when a test can detect it. The CDC says no HIV test can detect HIV immediately after infection. How long the window lasts depends on the test:
| Test type | Usual window (days after exposure) |
|---|---|
| NAT (nucleic acid test, blood from a vein) | 10 to 33 |
| Antigen/antibody test (lab, blood from a vein) | 18 to 45 |
| Antigen/antibody test (rapid, finger-prick blood) | 18 to 90 |
| Antibody test (includes most rapid tests and home self-tests) | 23 to 90 |
These are CDC figures for when a test can usually detect HIV. If you are unsure which applies to you, use the longer number. See our wider window periods guide for other infections.
Should I wait for a test if it was less than 72 hours ago?
No. If the exposure was in the last 72 hours, go for care and ask about PEP. The CDC says PEP must be started within 72 hours and that every hour counts. The first dose shouldn’t wait for a result. See HIV PEP: what to do in the first 72 hours.
How do the different HIV tests work?
- Antibody tests look for antibodies to HIV in blood or oral fluid. The CDC says antibody tests using blood from a vein can detect HIV sooner than tests using a finger stick or oral fluid.
- Antigen/antibody tests look for antibodies and for the p24 antigen, part of the virus, which can be found before antibodies develop. The CDC recommends these for lab testing.
- NATs look for the virus itself. The CDC says a NAT can detect HIV sooner than other tests and should be considered for people with a recent possible exposure and early symptoms who tested negative on another test.
Do home HIV tests work?
The CDC says an HIV self-test can be used at home or in a private location, with results in about 20 minutes. Most self-tests approved by the FDA are antibody tests, so they have the longest window: 23 to 90 days after exposure.
The FDA’s page on its approved oral-fluid home test is a good guide to what to expect:
- It checks for antibodies to HIV-1 and HIV-2 using a swab of the gums.
- Its expected sensitivity is about 92%, which the FDA says means about one false negative in every 12 results in people with HIV.
- Its specificity is 99.98%, which means about one false positive in every 5,000 results in people without HIV.
- The window period is about three months, and a negative result soon after an exposure should be repeated.
The FDA also says it can’t give assurance that unapproved tests are accurate, and the NHS advises using good quality home kits from a reliable source. If your exposure was recent, repeat the test later, once the window has passed.
What does a positive result mean?
A positive on a home test or any antibody test isn’t final. The CDC says that if you use any antibody test and get a positive result, you need a follow-up test to confirm it, and that after a positive self-test you should go to a health care provider. If the follow-up test is also positive, it means you have HIV. The FDA says confirmatory testing will either confirm a positive result or show that the first result was a false positive.
If you do have HIV, the CDC says to find HIV care and start treatment as soon as possible. It adds that treatment can bring the amount of HIV in your body so low that a test can’t detect it, and that people with an undetectable viral load will not transmit HIV through sex.
What does a negative result mean?
It depends on timing. The CDC says that if you get tested after a possible exposure and the result is negative, you should test again after the window period for your test type. If you test after the window period, have had no possible exposure since, and the result is negative, you do not have HIV.
Where can I get tested?
Order an HIV test online. Depending on the test, you either visit a nearby partner lab for a blood draw or use a kit at home, and you get results online. Check which type of HIV test it is, because that decides how soon after an exposure it can give a reliable answer. You can also buy a self-test online, but make sure it is an approved one, since the FDA cannot give assurance about unapproved tests. If a result is positive, see a health care provider for confirmatory testing and care.
Get care today if
- You think you were exposed to HIV in the last 72 hours (PEP must be started within 72 hours)
- You have a fever, rash, sore throat or swollen glands a few weeks after a possible exposure, and an earlier test was negative
- A home test or other rapid test came back positive. See a health care provider for a follow-up test
Call 911 for a medical emergency. Otherwise, urgent care or your doctor can see you today.
When to test
- Within 72 hours of a possible exposureAsk about PEP at an emergency room or urgent care clinic. Don't wait for a test to be possible. See our HIV PEP page.
- 10 to 45 days after the exposureA NAT (10 to 33 days) or a lab antigen/antibody test using blood from a vein (18 to 45 days) can usually detect HIV in this period. When you order an HIV test online, check which type it is.
- Up to 90 days after the exposureThis is the longest window for antibody tests, including home self-tests, and for finger-prick antigen/antibody tests. A negative result after this point, with no further exposure, is the most reliable.
Common questions
How soon after exposure can an HIV test be accurate?
It depends on the test. The CDC says a NAT can usually detect HIV 10 to 33 days after exposure, a lab antigen/antibody test 18 to 45 days, and a finger-prick antigen/antibody test 18 to 90 days. Antibody tests, including most home kits, take 23 to 90 days. A negative result taken before your test's window has passed should be repeated.
Are home HIV tests reliable?
The FDA says its approved home test is relatively reliable once enough time has passed for antibodies to develop. The FDA says its approved oral-fluid test has an expected sensitivity of about 92%, meaning about 1 false negative in every 12 results in people who have HIV, and a window period of about three months. It also says the FDA cannot give assurance about unapproved tests.
Can a home test be positive and then a lab test be negative?
It can happen. The CDC says a positive antibody test needs a follow-up test to confirm it, and the FDA says a small number of false positives happen even when directions are followed, roughly 1 in 5,000 results in people without HIV for its approved oral test. A health care provider can run the confirmatory testing.
What do the different HIV tests look for?
Antibody tests look for the immune system's response to HIV. Antigen/antibody tests look for that response and for a part of the virus itself (the p24 antigen), which can show up earlier. A NAT looks for the virus itself and can detect HIV sooner than other tests, according to the CDC.
Does a negative result mean I'm in the clear?
Only if the test was taken after its window period, with no possible exposure since. The CDC says a negative result doesn't necessarily mean you don't have HIV because of the window period, so retest after the window for your test type.
Sources
This guide is general information written by a patient advocate using public health sources. It is not a diagnosis. Only a clinician who examines you, or a lab test, can tell you what you have. Read how we write and check our guides.