Hi there.. The window period is time between potential exposure to HIV infection and the point when the test will give an accurate result. During the window period a person can be infected with HIV and infectious but have a negative for usual HIV test. It lasts upto 12 weeks.. after this time usual test ie Elisa( which detects HIV antibodies) til give accurate results.. Viral load and p24 antigen assay can be helpful in detecting HIV during window period but they also can detect only after 1-2weeks after exposure.. please consult nearest ICTC centre for complete evaluation, test details and treatment..