The window period for HIV is the period of time between infection with HIV and the time when the infection can be detected through a blood test. The window period varies for different people and different tests, and is likely to be fixed if it corresponds to a fixed person and a fixed test. However, for different people, there is a range of window periods for one test. Generally, it is performed using a test for HIV antibodies, and its window period is usually about three weeks, which may be prolonged in some people, but not more than twelve weeks. If the p24 antigen combined with HIV antibody test is used, which is a 4th generation test, the window period will be shortened. The shortened period is usually about two weeks, and if it is longer, it will not exceed six weeks.