Federal civilian employees may be compensated for periods of illness, disability, or injury through one of three systems: paid sick leave, disability retirement, or workers' compensation benefits for injuries sustained at work. In most cases, short-term illness or injury is compensated through paid sick leave. A federal employee who experiences a permanent disability can take a disability retirement before reaching the statutory retirement age. Disability retirement benefits differ between the two federal retirement systems: the Civil Service Retirement System (CSRS) and the Federal Employees' Retirement System (FERS). Federal employees hired before 1984 are covered by CSRS and those who were hired in 1984 or later are covered by FERS. Employees enrolled in CSRS do not pay Social Security taxes and do not earn Social Security benefits while employed by the federal government. Employees enrolled in FERS pay Social Security taxes and earn Social Security benefits. Until the age of 62, disability retirement annuities under FERS are offset in part by the amount of Social Security benefits the annuitant receives. Workers who experience short-term illnesses or injuries can use paid sick leave to take time off from work. Federal employees accrue sick leave at the rate of 4 hours for each two-week pay period up to a total of 104 hours (13 days) per year. Unused sick leave continues to accrue without limit throughout a federal employee's career. If an employee has exhausted his or her accrued sick leave balance, the worker's employing agency can advance up to 30 days of sick leave per year. Ill or injured workers who have exhausted their accrued sick leave but who expect to be able to return to work can use their accrued annual leave or, in some cases, can take leave without pay until they have recovered and can return to work. The federal government does not offer short-term disability insurance to workers who have exhausted their accrued sick leave and annual leave. The Federal Employees Leave Sharing Act of 1988 ( P.L. 100-566 ) authorizes a voluntary leave bank program through which federal agencies may allow employees to donate unused annual leave to employees who have exhausted their accrued sick leave. Employees cannot donate unused sick leave. When a worker covered by CSRS or FERS retires, any unused sick leave that he or she has accrued is added to the employee's length of service for purposes of computing the employee's annuity. A federal employee enrolled in CSRS is eligible for a disability retirement if he or she has completed at least five years of creditable civilian service; the employee has a disability that results in deficient performance, conduct, or attendance or that is incompatible with the individual continuing to perform useful and efficient service in his or her job; a physician certifies that the disability is expected to last a year or more; the worker's employing agency is unable to accommodate the disability in the worker's current job or in an existing vacant position at the same grade or pay and in the same commuting area; and an application for disability retirement is filed with the employing agency before separation or with the Office of Personnel Management within one year of the date of separation from employment. Unlike the eligibility requirements for benefits under the Social Security Disability Insurance Income (SSDI) and Supplemental Security (SSI) programs, eligibility for a CSRS disability retirement annuity does not require the employee to be disabled for any employment in the national economy. Instead, to be eligible for a CSRS disability retirement annuity, the employee must be unable to perform the job to which he or she was assigned or a job at the same pay in the same commuting area. Unless the Office of Personnel Management (OPM) certifies that the individual's disability is permanent, an employee who has retired due to disability is required to undergo periodic medical reevaluations until the age of 60. If the individual recovers, disability annuity payments continue temporarily while the individual seeks reemployment. The disability annuity terminates at the earliest of (1) the date on which the individual is reemployed by the government, (2) one year from the date of a medical examination showing that the individual has recovered from the illness or disability, or (3) six months from the end of the calendar year in which the individual demonstrates that his or her earning capacity has been restored. The individual's earning capacity is deemed to have been restored if, in any calendar year, his or her income from wages, self-employment, or both is equal to at least 80% of the current rate of pay for the position he or she occupied immediately before retiring. Under CSRS, a disabled worker is eligible for a retirement annuity equal to the greater of (1) the annuity that he or she would receive under the regular retirement formula, or (2) a minimum benefit that is the lesser of 40% of the average of the employee's highest three consecutive years of basic pay ("high-three" pay), or the annuity that would be paid if the employee continued working until the age of 60 at the same high-three pay, including in the annuity computation the number of years of service and the years between the date of retirement and the date on which the individual would reach the age of 60. The method of computing a CSRS disability retirement annuity assures that an employee will not receive a larger annuity through a disability retirement than he or she would receive from having worked to the minimum age and years of service required for a normal retirement. In general, a worker who becomes disabled after 22 or more years of federal service will receive an annuity computed under the regular CSRS annuity formula, regardless of his or her age. Because CSRS has been closed to new entrants since 1984, most federal employees covered by CSRS now have 30 or more years of service. Under CSRS, a regular retirement annuity for 30 years of service would replace 56.25% of the worker's high-three average pay. A federal employee covered by CSRS can take regular retirement with an immediate, unreduced annuity at the age of 55 or later with at least 30 years of service, at the age of 60 or later with at least 20 years of service, or at the age of 62 with at least five years of service. CSRS retirement annuities are indexed annually to the rate of growth of the Consumer Price Index (CPI), regardless of whether the individual retired due to disability or under normal retirement rules. A federal employee who is enrolled in FERS must have completed at least 18 months of service to be eligible for a disability retirement. All other eligibility rules for disability retirement under FERS are the same as under CSRS. Federal employees enrolled in FERS also are covered by Social Security, and the amount of a disability annuity under FERS is offset until the age of 62 by a portion of any Social Security Disability Insurance (SSDI) benefit that the individual receives. Federal employees covered by FERS who apply for disability retirement also must apply for Social Security disability benefits. Eligibility for Social Security disability benefits requires a determination by the Social Security Administration that the individual is unable to perform substantial gainful activity in any job in the national economy. Therefore, an individual covered by FERS may be determined to be disabled for purposes of his or her job with the federal government, but not with respect to other employment. In such a case, the individual would be eligible to receive a FERS disability annuity but be ineligible for SSDI. A federal employee who is disabled under both the FERS and Social Security statutes would be eligible to receive both a FERS disability annuity and a Social Security benefit, subject to the provisions of federal law integrating the two benefits. For federal employees under 62 years of age, the FERS disability retirement annuity in the first year of disability is 60% of the individual's high-three average pay minus 100% of any Social Security benefit that he or she is receiving. In years after the first year of disability, the FERS disability annuity is 40% of the individual's high-three average pay minus 60% of any Social Security benefit that he or she is receiving. The FERS disability annuity remains at that level—adjusted annually by the FERS cost-of-living adjustment—until the individual reaches the age of 62. When a FERS disability annuitant reaches the age of 62, the FERS annuity is adjusted to the amount that the individual would have received if he or she had continued to work until the age of 62. This ensures that an individual who retires from federal employment as the result of disability does not receive a higher annuity after this age than he or she would have received as the result of taking a normal retirement. The adjusted annuity at the age of 62 is equal to 1.0% of the individual's high-three average pay (increased by the FERS cost-of-living adjustments since the date of the disability retirement) multiplied by the sum of years of service performed before the date of disability retirement plus the number of years since that date. If the total number of years is 20 or more, the annuity is 1.1% of high-three average pay multiplied by this number of years. If an employee covered by FERS becomes disabled at the age of 62 or later, his or her FERS annuity is computed under the regular FERS retirement rules. In most cases, the adjusted FERS benefit payable at the age of 62 will be lower than the annuity that was paid before age 62. However, at the age of 62 and later, the offset to the FERS annuity for any Social Security benefits that the individual may be receiving will cease. Also, a worker who was receiving a FERS annuity but was not eligible for SSDI can apply for Social Security retired worker benefits at the age of 62, provided that he or she has completed the required 40 quarters of employment covered by Social Security. The Social Security benefit will compensate in part for the reduction in the FERS annuity.