FERS vs CSRS Calculator: How to Use It
CSRS produces a much larger pension than FERS on the same salary and service history. The comparison only makes sense once you account for Social Security, TSP matching, and the COLA difference that compounds over 25 years of retirement.
What this calculator does
The FERS vs CSRS Calculator computes the annual and monthly pension under both systems using the same high-3 salary and years of service inputs. It shows a side-by-side pension comparison, projects the lifetime payout at 20 and 30 years under each system using their respective COLA rates, and adds Social Security income to the FERS total to show the full three-legged picture.
The COLA projection is where the comparison gets interesting. CSRS uses a full CPI COLA. FERS uses the diet COLA, which falls 1 percentage point behind CPI whenever inflation exceeds 3 percent. The calculator uses 2.5% CPI with a 1.5% effective FERS COLA and 2.5% CSRS COLA as the default assumptions, producing a compounding divergence over 20 to 30 years.
What each input means
High-3 average salary
The average of your three consecutive highest-paid years of basic pay. For most federal employees approaching retirement, this is the average of the last three years. Basic pay includes locality pay but excludes overtime, bonuses, and awards. Both the FERS and CSRS calculations use the same high-3 figure, which is why entering it once produces comparable results on identical inputs.
Years of creditable service
Total creditable federal service for the pension formula. This includes civilian FERS or CSRS service, military service with a deposit paid, and certain other creditable periods. Part-time service is prorated for the pension calculation. The calculator applies this same service figure to both the FERS and CSRS formulas so the comparison is apples-to-apples.
Retirement age
Affects which FERS multiplier applies. FERS employees who retire at 62 or older with at least 20 years of service receive the 1.1% multiplier instead of 1.0%. CSRS does not have this distinction; it always uses the stepped formula regardless of retirement age. Entering a retirement age below 62 applies the 1.0% FERS multiplier; at 62 or older with 20-plus years, 1.1% applies automatically.
Estimated Social Security benefit
Used only for the FERS column total. CSRS employees typically receive no Social Security from their federal service, so the CSRS column shows pension income alone. The FERS column adds your stated Social Security estimate to the pension figure to show the combined income from both sources. Get this figure from ssa.gov/myaccount for the claiming age you plan to use.
COLA assumptions
The projected CPI rate and the resulting FERS diet COLA rate. At the default 2.5% CPI, CSRS retirees receive 2.5% annual increases and FERS retirees receive 1.5% (because 2.5% is between 2% and 3%, triggering the flat 2% FERS COLA cap). You can adjust the CPI assumption to model different inflation environments. At 2% CPI or below, both systems receive the same COLA and the divergence disappears.
Understanding the outputs
The side-by-side annual and monthly pension figures show the year-one difference under each system. On a $90,000 high-3 with 30 years of service, CSRS produces $50,625 per year (56.25% of $90,000) versus $27,000 for FERS at 1.0% or $29,700 at 1.1%. That gap is about $23,000 per year in pension income at retirement.
The 20-year and 30-year lifetime payout projections show cumulative benefits received under each system, incorporating the COLA divergence. Because CSRS starts higher and grows faster, the lifetime total gap widens each year. By year 20, a $90,000 CSRS pension at 2.5% COLA has grown to roughly $57,000 per year while the equivalent FERS pension at 1.5% COLA has grown to about $33,000.
The FERS total column adds Social Security to close part of the gap. Whether the FERS three-legged system (pension plus Social Security plus TSP) actually matches CSRS over a long retirement depends on Social Security earnings history, TSP investment behavior, and inflation. The calculator shows the pension and Social Security comparison. TSP requires separate modeling.
What CSRS doesn't have
CSRS employees pay no Social Security tax on federal wages and accrue no Social Security credits from that service. There is also no agency TSP matching for CSRS employees. They can contribute to the TSP on their own, but the government does not match those contributions. FERS employees receive up to 5% in agency matching (1% automatic plus 4% matched). Over a 30-year career, that matching difference compounds into a significant gap in total retirement wealth that offsets some of the CSRS pension advantage.
The survivor benefit difference
CSRS survivor benefits pay 55% of the unreduced annuity to a qualifying spouse. FERS survivor benefits pay 50% of the unreduced annuity. The cost structure also differs: CSRS charges 2.5% on the first $3,600 of annuity plus 10% on the remainder. FERS charges a flat 10% of the pension. On a larger CSRS pension, the absolute dollar value of the survivor benefit is substantially higher even though the percentage is only slightly more generous.
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Frequently asked questions
What is the CSRS pension formula?
CSRS uses a stepped accrual rate: 1.5% per year for years 1-5, 1.75% for years 6-10, and 2.0% for every year after 10. The benefit is capped at 80% of high-3, requiring roughly 41 years and 11 months. A 30-year CSRS employee accrues 56.25% of high-3 salary. FERS accrues 1.0% or 1.1% per year, so 30 years produces 30% to 33%.
What is the difference between the FERS diet COLA and the CSRS full COLA?
CSRS retirees get the full CPI increase every year. FERS retirees get a reduced COLA: full CPI when CPI is 2% or below, a flat 2% when CPI is between 2% and 3%, and CPI minus 1 point when CPI exceeds 3%. In a 4% inflation year, CSRS gets 4% and FERS gets 3%. Over 25 years of retirement, this 1-point gap compounds into a meaningful purchasing power difference.
Who is still on CSRS in 2026?
Only federal employees hired before January 1, 1987 who never switched to FERS. The youngest possible active CSRS employee is approaching 60 years old in 2026. Most are in their late 60s or already retired. Active CSRS participants are a small and shrinking share of the federal workforce.
Do CSRS employees get Social Security from their federal service?
No. CSRS employees do not pay Social Security taxes on federal wages. Some have Social Security from outside jobs. The Social Security Fairness Act of January 2025 repealed the Windfall Elimination Provision and Government Pension Offset, so CSRS retirees with Social Security from non-federal employment now receive higher SS payments than before the repeal.
Do CSRS employees get TSP matching contributions?
No. CSRS employees can contribute to the TSP but receive no agency matching. FERS employees get up to 5% in agency matching: 1% automatic plus dollar-for-dollar on the first 3% and 50 cents on the dollar for the next 2%. Over a 30-year career at $80,000 salary, that 5% match compounds to roughly $560,000 in additional wealth at 6% returns. That gap partially offsets the larger CSRS pension when comparing total retirement wealth across both systems.