If an hiv-positive tops an hiv-negative bottom with ejac, what is the percentage the bottom will seroconvert?

The risk is 0.5% assuming the 'top' is HIV+.
Practice safe sex.

This stat is correct. Please don't listen to people who have read a few journals and think they know all.

It realy depends. Did the top tear the bottom? Was their blood? How many times did it happen?? If it only happend once, you can lower the risk by not doing it again. repeated exposure definitely increases the risk. also there are stats about all this on the internet. do a search for "Hiv transmission rates." It wll describe all the different scenarios and how likely it is to catch it from a one time exposure. I think it was the CDC website or it could have been this HIV website i dont rmemeber the name now its like "positvie' or something. also the reason i ask fi the bottom bled, beuase that sggests their was an open route to the blood stream and that the ejaculate could have made direct contact. this significantly increases the risk. if the bottom knows FOR SURE that the top had HIV. there are some treatments they can do at the hosptial within the first fiew days after the exposure. they are called retroviral treatments or something. This is what they give health care workers who have an on the job exposure. The treatment is suppsed to significantly reduce the risk of catching it, but it must be done very soon after exposure, and im not sure how you would go about getting the treatment, other than going to the ER and say that the guy had HIV adn that you wer exposed etc... maek ti sound as dire as possible so they will take action. good luck

Can't give you a percentage, but I can tell you to wait three months and get tested. (Usually it won't show up before 90 days). You really need to use protection to help prevent the spread, in both oral, and penetrative activity. There's a good chance the bottom has caught it...unless he's lucky and escaped this one time.