I would say for most academic IM programs, approx 50-70% of graduates go into fellowship. (This is not based on any verified source, but just my experience). With that said, as other posters mentioned, this varies every year depending on what graduates that year want to do (fellowship vs. primary care/hospitalist) or where they want to live. A better number is what percentage of those who apply actually match. However, this is probably not a number that is published on websites and programs will just say "primary care/hospitalist" for those who don't match. That number also doesn't include those who are discouraged from applying. In any case, if OP is dead set on a fellowship, then I think going to a place where at least 20% of graduates consistently match into fellowships is reasonable.