I am curious as to how long an individual must hold a rank before one can retire at said rank? As I have mentioned before, I am contemplating the Navy's HSCP program. I have been trying to do a cost/benefit analysis to determine if it is worth it. If my understanding is correct I will only need to practice medicine for seven years in the Navy (beyond residency) to retire. My calculations are based on 20 years - 6 years active AF - 4 years HSCP - 3 years military residency (assuming a primary care specialty) = 7 years. Does this sound right? I am wondering if in those 10 years of commissioned services it is possible to achieve the rank of CDR (O-5). I believe I can be given time in grade credit for my MSPH. Even if I did make CDR in that time period would I be able to retire at that rank?