HIV Window Period
What we know about the window period:
It takes time for the body to produce enough antibodies for an HIV test to show that a person has HIV. The soonest an antibody test will detect infection is 3 weeks. Most, but not all people will develop detectable antibodies within 3 to 12 weeks of infection.
Most, but not all people will make enough antigens and antibodies for fourth generation or combination tests to accurately detect infection 13 to 42 days after infection.
Most, but not all people will have enough HIV in their blood for a NAT test to detect infection 7 to 28 days after infection. This is during the time when someone has acute HIV infection
What you can do
Let your health care provider know if you may have been exposed to HIV. Together, you can figure out the best type of HIV test you should have. Ask your health care provider about the window period for the test you're taking. If you're using a home test, you can get that information from the materials included in the test's package. If you get an HIV test within 3 months after a potential HIV exposure and the result is negative, get tested again in 3 more months to be sure.
If you think you've recently been exposed to HIV during sex (e.g., if the condom breaks or comes off) or through sharing needles and works to prepare drugs (e.g., cotton, cookers, water), talk to your health care provider or an emergency room doctor about taking post-exposure prophylaxis (PEP) right away. PEP must begin as soon as possible, and always within 72 hours (3 days) of a recent possible exposure.