1. High-3: If you entered active or reserve military service after September 7, 1980, your retired pay base is the average of the highest 36 months of basic pay. If you joined between Sept. 8, 1980, and July 31, 1986, you can use the High-3 Calculator to figure out your estimated base pay. 2. Final Pay: If you entered active or reserve military service before September 8, 1980, your retired pay will be based on your final basic pay. This retirement plan offers a pension after 20 years of service that equals 2.5% of your average basic pay for your three highest paid years, or 36 months, for each year you serve. Final Pay Calculator:This calculator estimates your retirement pay flow under the Final Pay retirement system including charts and tables based on your personal situation. 1. Military Retirement Calculator - Compare military retirement pay against different … How to use the High-3 military retirement calculator. Military Retirement Calculator - Compare military retirement pay against different retirement dates and ranks, estimate future pay for 40 years after retirement and automatically calculates early retirement pay if you enter a retirement date that is less than 20 years of service. Final Pay Calculator - This calculator estimates your retirement benefits under the Final Pay retirement plan, for those members who first joined prior to September 8, 1980.