The window period is he time it takes for the body to produce antibodies after someone has been infected wih the virus. In many cases this period can take btween 2 to 12 weeks, but there has also been cases where it can take up to 6 months. During this period you may be infected with HIV but your result can still be negative. It may take 3 months after exposure for the test results to be 97% accurate, and 6 months to be absolutely certain. If you feel you have been exposed to HIV, and your test results are negative, be sure to get retested in 3 to 6 months to be sure.