A qualified candidate with a nomination has about an 80% chance of an appointment.
Last year, 2099 qualified candidates were offered 1642 appointments.
Well, that 80% (which has sometimes been quoted as
78%, 1642/2099) is basically correct, but just bear in mind that about 350 of this year's applicants will be designated for a Prep year before entering the Academy. So, it looks more like, from the 3Q'd-with-a-Nomination applicants in the about-to-graduate-high-school pool, that about
62% will get direct appointments (the "four-year-program", entering with the Class of 2013) and about
13% will get offered either Falcon Foundation Prep or AFA Prep (the "five-year-programs", hoping to enter with the Class of 2014). Total is still around 75%, but a significant portion of that group will get a Prep offer rather than be offered a Direct Appointment.
Basically, about 300 acceptee slots are rolling over each year, as about 275 or so of last year's Preps successfully complete their year, and, in turn, about 350 of this year's applicants get offered Prep. If you get a Falcon Prep or AFA Prep offer, that's great news, but I think it overstates it to suggest that a 3Q'ed, Nominated current HS student has a 75% to 80% chance of a direct appointment. It looks like it's more like about a 62% chance of a Direct appointment, and about a 13% chance of a Prep offer (yes, that 75% doesn't add up to 78% or 80%; that's because a significant number of AFA Preps come out of Current Enlisted, which might be a separate pool).
I remember seeing another thread where someone said that of the entering class of 1200, about 800 come straight out of high school, and about 400 come from Prep or are otherwise at least one year out of high school. That seems accurate.