Under both CSRS and FERS, disability benefits are payable if you have become so disabled that you are prevented from performing useful and efficient service in your current position. Under law, to be eligible to apply for disability retirement, a FERS employee needs to have competed 18 months of creditable civilian service while a CSRS employee must have completed at least five years.
Note: Because CSRS was closed to new hires years ago and anyone leaving and later returning to the workforce as a CSRS Offset employee will already have five years under his belt, the latter provision is now moot.
To apply for a disability retirement, you must fill out a Standard Form 3112 and send it to the Office of Personnel Management. Your agency can help you do this. Concurrently, your agency will have to certify that it you can’t provide useful and efficient service in your present position, even with reasonable adjustments to your working conditions, and that it doesn’t have any less demanding vacant position in your commuting area that is at the same grade and pay. (Note: Collective bargaining agreements may impose certain additional conditions.)
Because they are covered by Social Security, CSRS Offset or FERS employees must also apply to the Social Security Administration for disability retirement. SSA has different and much higher standard for determining if you are disabled. To be judged disabled by SSA, you must be so severely disabled that you cannot perform any substantially gainful employment.
If you are a CSRS employee who is judged to be disabled, you will receive either 40 percent of your high-3 years of average salary or an amount that results from increasing your actual service from the date the disability retirement is approved to age 60. In effect, the 40 percent calculation is the guaranteed minimum you will get.
If you are a FERS employee under age 62, you will receive 60 percent of your high-3 minus any Social Security disability benefit to which you are entitled for the first 12 months. After that, the first figure is reduced to 40 percent minus 60 percent of the Social Security benefit.
Whether you are CSRS or FERS employee, if your earned benefit based on years of service is greater than these figures, you will get the higher amount. If you are a FERS employee, at age 62 your whole benefit will be recalculated as you had worked from the onset of the disability to age 62.
Deep dive: Phased Retirement for Federal Employees