Physicians, Dentists, Optometrists, Physician Assistants or Clinical Psychologists who participated in the Health Professions Scholarship Program (HPSP) and/or Financial Assistance Program (FAP) and drill in a critically undermanned subspecialty, can earn 1 year toward retirement for each year of drill, up to a maximum of 4 years. DoDI 1215.07 page 14
HPSP retirement example*: A CDR, who serves in a DoD Critical Wartime Specialty, participated in the HPSP program for 4 years and separates with 12 years of AD service. For each year the officer completes a satisfactory year towards Reserve retirement, the officer can convert 1 year of time served in HPSP to a qualifying year towards Reserve retirement. That CDR would need to serve in the SELRES for 8 years to reach retirement eligibility and if retires at that time, would be credited with 24 years (to include HPSP time). The first 2 years run concurrent with the 2-year involuntary mobilization deferment.