weeks to make antibodies against HIV, but tests differ in how early they are able to detect antibodies. Although most HIV tests look for these antibodies, some look for the virus itself. The period after infection but before the test becomes positive is called the window period.
Deciding when to get tested therefore depends on when you may have been exposed and which test is used. You can ask your health care provider about the window period for the HIV test you are taking. If you are using a home test, you can get that information from the materials included in the packaging of the test.
A few people will have a longer window period, so if you get a negative antibody test result in the first 3 months after possible exposure, you should get a repeat test after 3 months. Ninety-seven percent of people will develop antibodies in the first 3 months after they are infected. In very rare cases, it can take up to 6 months to develop antibodies to HIV.