Last odds I saw say that if a poz guy fucks you the overall odds are between 50 and 70 to 1 it will catch. Can catch on first try though. This is just overall odds they have found. Guy on meds and undetectable has had various results so far--from 0 chance as long as they take their meds properly to almost the same as no meds when they don't take meds properly. It was found a while back that a very large number did not take their meds as prescribed, leading to people getting HIV from them because of that. Saw a chart once that listed the 'best' way to catch HIV was from those saying they are Neg but not really testing, lol, followed by no meds and undetectable the lowest risk. Depends on other factors also. Cleanliness of your hole, or abrasions in there or around opening and so forth. You can catch it from oral, but only they have found, when you have abrasions or sores in your mouth or throat. Many factors go into it.