MS may or may not be used by OPM for disability retirement annuity (payable at any age) purposes. Although MS is rarely used to establish the 5-year minimum civilian service requirement, it may be used to compute the benefit amount.

A disability annuity will be computed under the general formula or under the guaranteed minimum annuity formula.

A disability retirement benefit is computed under the general (age and length of service) formula if it yields a higher benefit amount than the guaranteed minimum formula. Pre-1957 MS will be credited for eligibility or benefit amount purposes, and SS cannot grant wage credits.

A disability retirement benefit is computed under the guaranteed minimum annuity if it yields a higher benefit than the general formula. The guaranteed minimum is the lesser of the two following amounts:

1. a. 

   forty percent of the employee's high-3 average pay; or

2. b. 

   the amount obtained under the general formula after increasing the employee's actual creditable service by the time between the separation date and the date of attainment of age 60 (“service to age 60”).

Under the guaranteed minimum formula, an annuity based on 40 percent of the high-3 does not involve OPM's use of pre-1957 MS; thus, SS may grant wage credits. An annuity based on “service to age 60” will include pre-1957 MS and, as under the general formula, SS wage credits are precluded.

Because of the percentage and age limitations of the guaranteed minimum formula, that formula offers no advantage and will not be used if the employee:

1. a. 

   has completed at least 21 years and 11 months of service, including pre-1957 MS; or

2. b. 

   is age 60 or over at the time of separation.

Therefore, an employee who becomes disabled and meets either of the above service or age limits will have their annuity based on the general formula, pre-1957 MS will be credited, and SS cannot grant wage credits. SSA-655-U2 development to OPM is not required unless the length of service or age at separation is unknown or cannot be determined.