Most HIV tests are designed to detect the antibodies that the body produces to fight HIV once infection has occurred, but do not test for the virus itself. It can take some time for the immune system to produce enough antibodies for these tests to be able to detect them, and this time period can vary from person to person. Most people will develop detectable antibodies within three months, but it can take longer, including up to six months in some cases. This time period is known as the "window period", when an individual may be infected with HIV, but may not yet test positive.

There are several different types of approved HIV tests, including blood tests, oral fluid tests, and urine tests. Some tests, called rapid tests, can provide results within 20-30 minutes. The availability of HIV testing and these different kinds of tests will vary depending on where you live.