I have found that a rough estimate is by comparing the number of applicants interviewed to the number of spots offered at the programs you are applying to. FREIDA has this information for most programs. In general, most programs will interview at a ratio of 10 applicants for 1 spot. Some may do more, some may do less. In general, and using this logic, I am using 1 in 10 as a rough estimate, meaning that 10 interviews puts me in line with my odds. However, a PD at a large institution has told me that overall, 12 interviews will provide most candidates with a 95% match outcome rate.