CSRS — the Civil Service Retirement System, the older defined-benefit pension that predates FERS — is rarely the primary system of anyone reading this article who is still actively employed. It closed to new enrollees on January 1, 1987. But the system is still alive, and a meaningful number of federal employees in 2026 are on it: employees who were hired before 1984 and never switched to FERS, employees who had a break in service that preserved their CSRS coverage, and a smaller number of employees who were rehired after a CSRS separation and reinstated their CSRS enrollment.

For those employees, and for the spouses and survivors trying to understand their annuity calculation, the CSRS formula is the single most important number on the page.

CSRS is not FERS, and the difference shows up in the formula.

FERS gives you 1% of your high-3 per year of service (with the 1.1% enhancement for the first 20 years when you retire at 62 or later). CSRS gives you more. The standard CSRS formula is:

1.5% × first 5 years of service × High-3 + 1.75% × remaining years of service × High-3

Two tiers, two different multipliers, and a noticeably steeper accrual than FERS. That is the headline.

The arithmetic, written out.

A CSRS employee retiring with 30 years of service and a $100,000 high-3 receives:

  • 1.5% × 5 × $100,000 = $7,500
  • 1.75% × 25 × $100,000 = $43,750
  • Total: $51,250 per year

A FERS employee with the same 30 years and the same $100,000 high-3 who retires at 62 (and qualifies for the 1.1% block on the first 20 years) would receive $44,000. If they retire before 62, the FERS employee receives $30,000.

The CSRS number is significantly larger. That is not a coincidence. CSRS was designed as a more generous system because it does not include Social Security. CSRS employees pay a larger payroll contribution (roughly 7% of pay, vs. about 0.8% for FERS most years) and they do not earn Social Security credits on their federal service. The pension was the trade.

The 80% maximum is the wall that the formula runs into.

The CSRS formula can compound impressively — but it cannot compound without a ceiling. The maximum CSRS annuity, before any reductions, is 80% of your high-3 average salary. For a CSRS employee with a $100,000 high-3, that is $80,000 per year, before survivor reductions.

The 80% cap is reached at different service totals depending on your high-3. The math is a function of the two-tier formula and the cap. A useful frame: an employee with 41 years and 11 months of service on a typical high-3 will generally max out the formula.

We will dig into the cap in a separate article, because it has its own set of behaviors and edge cases.

The CSRS formula interacts with several adjacent decisions.

The formula itself is mechanical, but the real-world implications of being on CSRS are not. Three things every CSRS employee should know:

1. The survivor election math is different from FERS.

A full CSRS survivor annuity also reduces your own annuity by roughly 10%, but the maximum survivor benefit under CSRS is 55% of your unreduced annuity, and the partial survivor benefit produces 25% — slightly different from the FERS 50%/25% structure. The cost calculations are similar; the outputs are not identical.

2. The high-3 is calculated the same way, but it often matters more.

CSRS employees have higher pension accrual per year, which means that an additional year of high-3 salary at the end of a career moves the annual annuity more meaningfully. A 1.5% or 1.75% multiplier on a $130,000 high-3 is real money; a 1.0% multiplier on the same high-3 is less. Working one more year in CSRS is, dollar-for-dollar, a bigger pension decision than working one more year in FERS.

3. The CSRS offset variant is its own system.

Employees who switched from CSRS to FERS (or were hired into positions that were converted to FERS) but who retained a “CSRS component” are on the CSRS Offset system. Their pension is calculated partly under CSRS rules and partly under FERS rules, and the Social Security earnings from their federal service are used to offset the CSRS portion at age 62. That is a separate article.

What the formula doesn’t include.

The CSRS annuity calculation does not include the FERS supplement (which doesn’t exist in CSRS), it does not include the TSP match (CSRS employees get TSP matching only under specific FERS-TSP rules), and it does not include Social Security (which is the whole point of the more generous accrual). It also doesn’t include the FEGLI, FEHB, or any other benefits.

For CSRS employees, the pension is the foundation, and Social Security is largely absent. That single fact is the reason the CSRS formula was built to be more generous, and it is also the reason the retirement-income conversation for CSRS employees looks different from the same conversation for FERS employees.

Why the formula is a starting point, not a final answer.

The CSRS formula is precise, but the formula’s inputs are not always clean. Service computation dates include deposits for prior service, redeposits for refunded contributions, military service deposits, and a long list of edge cases. Unused sick leave is credited differently under CSRS than under FERS. The high-3 calculation, while mechanical, can be distorted by within-grade raises, locality pay changes, and shift differentials.

The OPM annuity estimate — the formal one, generated from your official personnel folder and your service computation — is the source of truth. The formula described in this article gives you a working estimate, not a final number.