Federal civilian retirement in the United States is split between two defined-benefit systems that use different formulas, different contribution rates, and different rules for inflation adjustment. The Civil Service Retirement System (CSRS) covered employees hired before January 1, 1984, and the Federal Employees Retirement System (FERS) covers everyone hired on or after that date, plus rehires who returned after a break of more than 365 days. Although CSRS was closed to new entrants more than four decades ago, several hundred thousand CSRS employees and annuitants remain on the rolls, and the differences between the systems still drive millions of dollars in annual decisions about when to retire, whether to convert to FERS, and how to coordinate TSP, Social Security, and FEHB.
Why two systems still coexist
CSRS was created in 1920 and operated for more than 60 years as a standalone federal pension. It paid generous benefits — often 70% to 80% of high-3 salary for a full-career employee — and was funded entirely by employee and agency contributions, with no Social Security participation. By the early 1980s, Congress had concluded that the system was actuarially unsustainable, that federal employees lacked portable retirement benefits comparable to the private sector, and that the government was paying into a parallel retirement structure while also being required to extend Social Security coverage to new federal hires.
The Federal Employees' Retirement System Act of 1986 (Public Law 99-335) created FERS effective January 1, 1987, but the coverage cutoff was backdated to January 1, 1984, so that employees hired on or after that date would be covered by Social Security from their first day. Existing CSRS employees were permitted to remain in CSRS, and Congress later offered two open seasons — in 1987 and 1998 — to allow CSRS employees to transfer to FERS. Very few did, primarily because the CSRS annuity is substantially more generous for employees who spend a full career in federal service.
Today, the Office of Personnel Management reports that fewer than 50,000 active CSRS employees remain, out of a federal civilian workforce of roughly 2.1 million. The system is shrinking by retirement and attrition, but the annuitant rolls are still much larger — around 470,000 CSRS annuitants in 2025 — and CSRS rules will continue to affect payroll, benefits administration, and estate planning for at least another generation.
The CSRS structure
CSRS employees contribute 7.0% of basic pay to the retirement fund, with no Social Security withholding. The annuity formula is a tiered structure that produces an unusually high replacement rate for long-service employees. The first five years of service are multiplied by 1.5%, the next five years by 1.75%, and all years over ten by 2.0%. The maximum annuity is 80% of high-3 salary, reached at 41 years and 11 months of service.
For a 30-year employee, the formula produces 1.5% × 5 = 7.5%, plus 1.75% × 5 = 8.75%, plus 2.0% × 20 = 40%, for a total of 56.25% of high-3. The same employee under FERS would receive 30% of high-3 (or 33% if retiring at 62 or later with at least 20 years) — less than 60% of the CSRS amount. The CSRS employee also typically retired with a much smaller TSP balance because CSRS employees did not receive matching contributions until the late 1980s.
CSRS employees who retire with at least 30 years of service can retire as early as age 55 with a full annuity. The age 55 + 30 combination is more generous than any FERS option, and the absence of any FERS-style "MRA + 10" reduction made CSRS attractive to employees who wanted to retire early without penalty. CSRS annuities are also inflation-adjusted from the moment of retirement — no diet-COLA, no waiting period — which is one of the most valuable features of the system over a long retirement.
The FERS structure
FERS replaced the standalone CSRS pension with a three-legged model: a smaller defined-benefit annuity, mandatory Social Security coverage, and the Thrift Savings Plan (TSP) as a defined-contribution component with agency matching. The basic FERS multiplier is 1.0% per year of service, rising to 1.1% only for employees who retire at age 62 or later with at least 20 years. Special category employees — law enforcement, firefighters, air traffic controllers — receive a 1.2% multiplier after 20 years.
FERS employee contribution rates have risen twice since the system was created. Original FERS employees (hired before January 1, 2013) contribute 0.8% of basic pay. FERS-RAE employees, first hired in calendar year 2013, contribute 3.1%. FERS-FRAE employees, first hired on or after January 1, 2014, contribute 4.4%. The contribution differences produce no difference in the annuity formula — the higher rates are purely a payroll tax used to reduce the federal deficit.
Because the FERS annuity is smaller, the system depends more heavily on Social Security and TSP. A career FERS employee who contributes 5% of pay to TSP and captures the full agency match can build a TSP balance large enough to fill the gap between the FERS annuity and the CSRS replacement rate. But the FERS employee bears the investment and longevity risks that CSRS shifted entirely to the government. The TSP account can be exhausted; the CSRS annuity cannot.
CSRS Offset: the hybrid arrangement
CSRS Offset is a separate sub-system that affects employees who had at least five years of CSRS-covered service before January 1, 1984, left federal service for more than 365 days, and then returned to federal employment after 1983. These employees, upon rehire, are covered by both CSRS and Social Security. They pay into Social Security (6.2% of pay) and into the CSRS fund at a reduced rate of 0.8%, for a combined payroll deduction of 7.0% — the same total as a regular CSRS employee.
The "offset" occurs at retirement. Once the CSRS Offset annuitant becomes eligible for Social Security (typically at age 62), the CSRS annuity is reduced by the amount of Social Security benefit attributable to the years of CSRS Offset service. The reduction is calculated using a formula in 5 U.S.C. § 8334(k) and effectively prevents the employee from "double-dipping" — receiving both a full CSRS annuity and a full Social Security benefit for the same years of work.
In practice, CSRS Offset employees generally come out slightly ahead of pure CSRS employees, because they accrue Social Security credits that can be claimed on their own record or as a spousal/survivor benefit, and because the offset is computed based on the Social Security benefit attributable to offset service only — not their total Social Security benefit. Many CSRS Offset retirees also qualify for Social Security benefits from non-federal employment, which are paid in full without offset.
Open seasons and why so few switched
Congress authorized two open seasons during which CSRS employees could elect to transfer to FERS. The first ran from January 1, 1987 through June 30, 1987, immediately after FERS took effect. The second, longer open season ran from July 1, 1998 through December 31, 1998, after Congress concluded that few employees had understood the original election. In total, fewer than 5% of eligible CSRS employees transferred to FERS, even though OPM and outside financial planners argued that FERS was a better fit for employees who might leave federal service early or who wanted Roth-style accumulation in TSP.
The reasons for low participation varied. CSRS employees who were near retirement had little incentive to switch — their CSRS annuity was already locked in at the higher rate, and switching to FERS would have meant losing years of credit toward the generous CSRS formula. Younger CSRS employees were also reluctant, in part because TSP was brand new in 1987 and there was no track record of investment returns to compare with the certainty of a CSRS pension. By 1998, TSP had been around long enough to demonstrate real returns, but most employees who had not switched in 1987 had already decided to remain in CSRS.
For employees who did switch during the 1998 open season, OPM calculated a "FERS Transfer Redeposit" that allowed them to recapture some of the additional annuity value they would have earned under CSRS, less the higher FERS contributions they were now making. The transfer rules were complex enough that most employees who switched used a financial planner or attorney to model the decision.
COLAs, TSP, and Social Security differences
Three operational differences between CSRS and FERS continue to matter most to current retirees. First, COLAs: CSRS annuitants receive a full CPI-W cost-of-living adjustment from the moment they retire, regardless of age. FERS annuitants receive no COLA until age 62, and even then receive a "diet COLA" — 2% if CPI-W is between 2% and 3%, or CPI-W minus 1% if CPI-W is 3% or higher. Over a 25-year retirement, the diet-COLA can cost a FERS annuitant 15% to 20% of purchasing power compared with a CSRS annuitant with the same starting benefit.
Second, TSP matching: CSRS employees receive only the 1% agency automatic contribution, with no match on their own contributions. FERS employees receive the 1% automatic contribution plus a dollar-for-dollar match on the next 3% and a 50% match on the next 2%, for a total of 5% agency contribution when the employee contributes at least 5%. The 4% matching difference, compounded over a career, can amount to $100,000 or more in additional retirement savings for a FERS employee.
Third, Social Security: CSRS employees do not pay into Social Security and generally do not receive Social Security benefits based on their own federal earnings — but they may receive spousal or survivor benefits, which are subject to the Government Pension Offset (GPO) and Windfall Elimination Provision (WEP). The GPO reduces spousal/survivor Social Security benefits by two-thirds of the CSRS annuity, often to zero. The WEP reduces the employee's own Social Security benefit from non-federal work, capped at a 2025 reduction of $627 per month. The Social Security Fairness Act of 2023 repealed both the GPO and WEP effective January 5, 2025, which has materially increased Social Security payments for hundreds of thousands of CSRS annuitants with non-federal work histories.
For a fuller walkthrough of the modern system, see our FERS retirement guide, and to estimate your own FERS annuity, try our FERS pension calculator.
Last reviewed July 1, 2026. This article is informational and does not constitute legal, tax, or financial advice. Consult a qualified professional for guidance specific to your situation.