Which system you are in
Your Date of Initial Entry into Military Service (DIEMS) and your elections decide it. On or after January 1, 2018: the BRS, 2.0 percent per year. Before that: the BRS if you elected it, CSB/REDUX if you accepted the Career Status Bonus (entry August 1, 1986 – December 31, 2017; no new agreements after 2017), and otherwise legacy High-3 at 2.5 percent per year for a DIEMS on or after September 8, 1980. Before September 8, 1980 it is Final Pay, with your final basic pay as the base (DoD FMR Vol 7B Ch 1 ¶2.2.1, ¶2.3).
How the figure is built
Multiplier × high-3. The multiplier is 2 percent (BRS) or 2.5 percent (High-3) per year of creditable service, rounded to 1/100 of a point; REDUX subtracts 1 point for each year short of 30 and is restored at age 62 (FMR Vol 7B Ch 3 ¶2.1.2, ¶2.8.4, ¶2.10.2). Reserve and Guard years are total points ÷ 360. The result is rounded down to the dollar.
The BRS adds Thrift Savings Plan contributions, continuation pay and an optional lump sum: see the BRS calculator. For the Reserve start age and reduced-age credit, see the Reserve retirement calculator.
