How long does HIV take to show up on a test, after a first infection?

Average is 25 days. After an exposure to hiv, most people (if they become hiv-positive) will develop antibodies that can be detected by HIV tests sometime between 2 to 8 weeks with the average of 25 days. 97% will develop detectable antibodies within 3 months and the rest may develop antibodies as late as 6 months (though very rare). This is why we typically recommend repeating HIV tests every 6 months if at risk.