FERS vs CSRS: The Formulas Side by Side (1%/1.1% vs 1.5/1.75/2%, the 80% Cap, Special Provisions)

Updated 2026-10-12 · Based on OPM's CSRS/FERS Handbook and 5 U.S.C. · Estimate, not advice

The two federal retirement systems compute an annuity from the same ingredients, the high-3 and years of service, but the multiplier is very different. FERS pays a flat 1% of the high-3 for each year (1.1% in one case), and CSRS pays 1.5%, 1.75% and 2% in tiers and stops at 80%. CSRS was closed to new employees at the end of 1983, so today it matters for longtime employees, for people who retired from CSRS and for anyone comparing a spouse's benefits, while FERS applies to everyone hired since. This guide lays the formulas side by side, works the same $100,000 high-3 through both, and covers the special provisions, reductions, survivor elections and COLAs where the systems differ.

When you can retire

	FERS (voluntary)	CSRS (voluntary)
Unreduced	Age 62 with 5 years; age 60 with 20 years; minimum retirement age (MRA) with 30 years	Age 62 with 5 years; age 60 with 20 years; age 55 with 30 years
Reduced for age	MRA with 10 years (MRA+10): 5% a year under 62	None for voluntary retirement
Early (VERA or discontinued service)	Age 50 with 20 years, or any age with 25: no age reduction	Age 50 with 20 years, or any age with 25: reduced 2% a year under 55
Special provisions	Age 50 with 20 years of special service, or any age with 25	Age 50 with 20 years

The main difference is that CSRS has no MRA+10 route: its unreduced ages are lower (55 with 30 years against FERS's MRA of 55 to 57) and the early-retirement reduction applies to VERA and discontinued-service cases rather than ordinary voluntary ones. See the MRA+10 guide for the FERS reduction.

The multipliers

FERS regular: 1% of the high-3 for each year and month of service. If you are 62 or older at separation with 20 years or more of service (sick leave credit counts toward the 20), the multiplier is 1.1%. The age is measured at separation, so someone 61 years 11 months old with 25 years gets 1.0%.

FERS special provision (law enforcement officers, firefighters, CBP officers, nuclear materials couriers, air traffic controllers): 1.7% of the high-3 for each of the first 20 years and 1% for each year after. The 1.1% rule never applies to special-provision service.

CSRS regular: 1.5% of the high-3 for each of the first 5 years, 1.75% for each of the next 5, and 2% for each year over 10, capped at 80% of the high-3.

CSRS special provision: 2.5% for each of the first 20 years and 2% for each year after.

All of these are applied to the high-3 as a factor rounded to six places (OPM's accrual charts are printed that way), then the dollar annuity is rounded to the cent. The rounding is why OPM's Chris Morgan example is $16,587.23 and not $16,587.21.

Same pay, same service, two annuities

Using a $100,000 high-3 and no other adjustments:

Service	FERS at 1.0%	CSRS
5 years	$5,000	$7,500
10 years	$10,000	$16,250
20 years	$20,000	$36,250
25 years	$25,000	$46,250
30 years	$30,000	$56,250
35 years	$35,000	$66,250
40 years	$40,000	$76,250

The 30-year CSRS figure is OPM's published example: 5 years at 1.5% (7.5%), 5 at 1.75% (8.75%) and 20 at 2% (40%) is 56.25%, or $56,250 a year and $4,687 a month once the annual figure is divided by 12 and rounded down. FERS is a smaller percentage because it is one part of a three-part retirement: a FERS employee also has Social Security and the Thrift Savings Plan with an agency match, and CSRS employees (other than CSRS Offset) pay no Social Security tax on their federal pay and earn no Social Security credit from it. Comparing the two annuities alone therefore understates FERS.

The 80% cap, and sick leave on top of it

CSRS limits the annuity to 80% of the high-3. With the tiers above, the cap is reached at about 41 years 11 months, so 42 years of service on a $100,000 high-3 produces $80,000 rather than $80,250. Unused sick leave is added after the cap is applied, and each year of sick leave credit is worth 2%. OPM's example is a retiree with 43 years of service and 1 year of sick leave: the 43 years are capped at 80% and the sick leave adds 2%, for 82%. There is no cap on FERS, which is why nobody gets to the point of a cap there.

Where FERS gets bigger: the 1.1% rule

The extra 0.1% is easy to overlook and large. For a FERS retiree at age 62 with exactly 20 years 0 months and a $100,000 high-3, the multiplier is 1.1% and the annuity is $22,000. With 19 years 11 months at the same age it is 1.0% and the annuity is $19,916.70. One month of service is worth $2,083.30 a year at the 20-year line. For someone retiring at 62, the sick leave credit can push a balance across the line: it counts toward the 20 years for this purpose, though not for eligibility.

Special provisions in numbers

Case	Calculation	Annuity
FERS special, 25 years, $120,000 high-3, age 50	(1.7% x 20) + (1% x 5) = 39%	$46,800 a year, $3,900 a month
FERS special, 20 years, $100,000	1.7% x 20 = 34%	$34,000
FERS special, 25 years, $100,000, age 62	39%, not 1.1%	$39,000
CSRS special, 25 years, $100,000	(2.5% x 20) + (2% x 5) = 60%	$60,000

The third row is a reminder that the 1.1% rule does not apply to special-provision retirements; at 62 with 25 years the factor is still 1.7% and 1%. Special-provision retirees also receive the FERS supplement from retirement and are exempt from its earnings test until the minimum retirement age (supplement guide).

Age reductions

FERS MRA+10 retirements are reduced by 5/12 of 1% for each full month under 62 on the commencing date, with exceptions at 30 years and at 20 years at age 60 or older. CSRS early retirement, which covers VERA and discontinued service, reduces the annuity by 1/6 of 1% per full month under 55, which is 2% a year. For a CSRS retiree who is exactly 52 years 6 months 0 days old, the count is 30 months, the reduction is 5%, and $56,250 becomes $53,437.50 a year, $4,453 a month. FERS early retirement carries no age reduction, and neither does a special-provision retirement in either system.

Survivor elections

FERS lets you leave a survivor annuity of 50% of a base at a cost of 10% of that base. With a full election the base is the whole annuity: Chris Morgan's $16,587.23 becomes $14,928.51 a year ($1,244 a month) and his survivor gets $691 a month. A partial election uses half the annuity as the base, so the cost is 5% of the annuity. On a $30,000 annuity that leaves $28,500 and a survivor annuity of $7,500 a year, $625 a month.

CSRS survivor annuities pay 55% of a base the retiree chooses, with a reduction of 2.5% of the first $3,600 of the base and 10% of the rest. On a $14,000 annuity with the full amount as the base, the reduction is $1,130 (about $90 on the first $3,600 plus $1,040 on the rest), the retiree receives $12,870, and the survivor receives $7,700. With a $3,000 base the reduction is $75, the retiree receives $13,925 and the survivor receives $1,650.

In both systems the age reduction comes first and the survivor election is calculated on the reduced annuity.

COLAs

CSRS annuities get the full percentage increase in the CPI-W. FERS annuities follow a three-step rule under 5 U.S.C. 8462: if the CPI-W increase is 2% or less, FERS gets the same percentage; if it is between 2% and 3%, FERS gets 2%; and if it is above 3%, FERS gets the CPI-W minus 1 point. For the 2026 adjustment, CSRS received 2.8% and FERS received 2.0%. At a 3.5% CPI-W increase CSRS would get 3.5% and FERS 2.5%. FERS COLAs are generally not paid to regular retirees under 62; special-provision, disability and survivor annuities are exceptions.

CSRS Offset

A CSRS Offset employee is covered by Social Security for part of their federal career. At 62 the CSRS annuity is reduced by the lesser of two amounts: the Social Security benefit attributable to the offset service, or the Social Security benefit at 62 times the offset years (rounded to the nearest whole year) divided by 40. For example, 6 years of offset service and a $500 Social Security benefit give $500 x 6/40 = $75; if the attributable amount is $100, the lesser, $75, is the reduction. The free calculator does not compute the Offset; the app does.

Using the calculator

Pick FERS or CSRS in the free calculator and keep every other input the same to see the two annuities side by side. Switching the category to "Special provision" shows the 1.7% (FERS) and 2.5% (CSRS) first-20-year tiers once your age and service meet the special-provision test. Citations: OPM's FERS and CSRS computation pages; Handbook Chapter 50, sections 50A3 (CSRS) and 50B3 (FERS); 5 U.S.C. 8339, 8415 and 8462. Estimate, not advice: your agency's HR office and OPM compute your actual annuity.