The window period is the time between an HIV infection and the point when a test will give an accurate result.
During the window period a person can be infected with HIV and be very infectious but still test as HIV-negative.
Research indicates that 4 weeks after an HIV infection, about half of people have developed HIV antibodies. By 6 weeks after an HIV infection about 95% of people have developed HIV antibodies, however some people do not develop these HIV antibodies, until up to 12 weeks after an HIV infection. Therefore, it is important not to rely on a negative test result until 3 months after your most recent possible exposure to HIV.