The tests commonly used to detect HIV infection actually look for antibodies produced by your body to fight HIV. Most people will develop detectable antibodies within 3 months after infection, the average being 25 days. In rare cases, it can take up to 6 months.

For this reason, it is recommended to test 6 months after the last possible exposure (unprotected vaginal, anal, or oral sex or sharing needles). It would be extremely rare to take longer than 6 months to develop detectable antibodies.

It is important, during the 6 months between exposure and the test, to protect yourself and others from further possible exposures to HIV. The time it takes for a person who has been infected with HIV to seroconvert (test positive) for HIV antibodies is commonly called the "Window Period".