Reference:
Disability Retirement <---LINK
Disability retirement is sometimes called Chapter 61 retirement, since the law governing such a retirement is in Chapter 61 of title 10 United States Code. Members who have been determined to be unfit for duty with a disability rated by the military Service as 30% or greater are eligible for disability retirement. A member whose condition is not stable may be placed on the temporary disability retired list (TDRL) for up to five years at which point they must be either discharged, retired or returned to duty. Members whose condition has stabilized at a disability rating of 30% or higher may be placed on the permanent disability retired list (PDRL).
The basic retirement formula is:
Retired Pay Base X Multiplier %
The retired pay base for a qualified disability retirement is determined under either the final pay method or the high-36 month method depending upon when they first entered military service. See Retirement tab for details.
The multiplier percentage is at the option of the member who may chose either the percentage of disability assigned or the years of creditable service times 2½%. In either case, the multiplier is limited to 75% by law.
In the case of a member on the TDRL, the minimum percentage is 50% while on the TDRL.
Years of Service
The years of creditable service for computation of the retired pay percentage multiplier include all active duty and all credited reserve points divided by 360.
[The same would apply to the computation of the longevity portion of retired pay for CRSC purposes.]
Ron
Edited to add, from another source:
Reserves: Computation of Retired Pay (non-disability or longevity portion of disability retired pay)
To determine how much
retired pay you may be eligible to receive, the first step is to calculate the number of equivalent years of service. The formula for computing equivalent years of service for Reserve retired pay at age 60 is fairly simple:
Total number of Creditable Retirement Points, divided by 360.
The formula computes the number of equivalent years of service the soldier has completed (comparable to full-time service). For example, 3,600 points equals 10 years.
Military Personnel will notify the Defense Finance & Accounting Service – Cleveland Center (DFAS-CL) of the number of years service you’ve earned.