FERS Eligibility and Computation
To be eligible for a FERS retirement, you must have performed at least five years of creditable civilian service, sseparate from a FERS-covered position, and meet certain age and length of service requirements.
The amount of your annuity is based on two factors:
1) Your length of service
2) Your high-3 average salary
All periods of creditable civilian and military service, plus your unused sick leave, are totaled and used to determine your length of service for annuity computation purposes. Your high-3 average salary is the largest annual rate resulting from averaging your rates of pay in effect over any 3 consecutive years of creditable civilian service, with each rate weighted by the length of time it was in effect.
Your annuity will be computed using one of the following forumulas:
If you are under age 62, or over age 62 with less than 20 years of service.
= [1%] x [high-3 average salary] x [years of creditable service]
If you are age 62 or older and have at least 20 years of service
= [1.1%] x [high-3 average salary] x [years and months of creditable service]
Additional information is available on the OPM website.