How Is the FERS Supplement Calculated? Formula, Eligibility, and Offsets

The FERS supplement is calculated by taking your years of FERS-creditable civilian service, dividing by 40, and multiplying that fraction by an estimated Social Security benefit built only from your federal wages.¹ The result is a monthly payment that bridges the gap between your retirement date and age 62. OPM runs the numbers automatically as part of your retirement claim; you do not file a separate application.

The Formula

Two numbers drive everything: your creditable FERS service (the numerator, capped at 40) and a deemed age-62 Social Security benefit based only on your federal earnings. Divide the service years by 40, then multiply by the deemed benefit.²

A worked example. You retire with 28 years of FERS-creditable service, and OPM estimates your age-62 Social Security benefit at $1,800 based on federal wages alone. 28 ÷ 40 = 0.70. $1,800 × 0.70 = $1,260 per month. Change the service years to 35 and the same $1,800 estimate produces $1,575 per month. Each full year in the numerator moves the supplement by 2.5 percent of the deemed benefit.

Which Years Actually Count

The numerator is your civilian FERS service, rounded to the nearest whole year.³ Seven months or more rounds up; five months rounds down. Several kinds of service that boost your basic annuity are stripped out here:

Bought-back military service does not count, with a narrow exception for military time performed during an approved leave without pay from a civilian FERS position.¹
Unused sick leave, which converts to extra months on your basic annuity, does not factor in.
Part-time service is prorated. Ten years at half-time counts as roughly five years toward the numerator.

The upshot: the service number OPM plugs into the supplement formula is usually smaller than the total service printed on your retirement estimate. If a substantial share of your career was military time you later bought back, the gap can be large.

Where the Social Security Estimate Comes From

The second number in the formula is not the estimate on your annual Social Security statement. OPM constructs its own figure using only wages earned during FERS-covered employment.⁴ Private-sector wages, self-employment income, and earnings from non-FERS federal jobs are excluded.

OPM then applies the same indexing and benefit rules the Social Security Administration uses, but to that narrower earnings history. The output is a hypothetical age-62 primary insurance amount reflecting what you would receive if federal pay had been your only lifetime income. It is almost always lower than the number on your SSA statement, sometimes by a wide margin, because the SSA statement counts every covered job you have ever held. Budgeting from the SSA number will overstate the supplement.

Who the Calculation Applies To

OPM only runs the formula for retirees who fall into specific eligibility categories:⁵

Retirement at your Minimum Retirement Age with 30 years of service. MRA runs from 55 (born before 1948) to 57 (born in 1970 or later); most people retiring in 2026 have an MRA of 56 and 10 months or 57.⁶
Retirement at age 60 with 20 years of service.
Involuntary separation at age 50 with 20 years during a reduction in force or major reorganization, or a discontinued service retirement.
Special-category employees (law enforcement officers, firefighters, air traffic controllers, military reserve technicians, and certain SES members) under separate age-and-service rules.

Three common paths get nothing. MRA+10 retirements, deferred retirements, and disability retirements are all excluded.⁵ If you fall into one of those categories, the formula never runs for you at all.

What Can Shrink the Calculated Amount

Once OPM sets the supplement, two things can eat into what you actually receive.

The first is the earnings test. If your earned income exceeds the annual Social Security exempt amount, OPM reduces the supplement by $1 for every $2 you earn above the threshold.⁷ For 2026 the exempt amount is $24,480.⁸ Only wages and net self-employment income count. TSP withdrawals, investment income, rental income, your FERS annuity, and Social Security benefits do not.

An example: your calculated supplement is $1,200 per month, or $14,400 a year, and you earn $34,480 at a post-retirement job in 2026. You exceeded the exempt amount by $10,000. Half of that, $5,000, comes off the supplement the following year, roughly $417 per month. Large enough excess earnings can zero the supplement out, though the reduction never touches your basic FERS annuity.³ Law enforcement officers, firefighters, and air traffic controllers who retire before MRA under special provisions are not subject to the earnings test until they reach their MRA.

The second is inflation. The supplement receives no annual cost-of-living adjustment.⁹ The dollar figure OPM calculates on the day you retire is the same dollar figure you receive five years later. Over a bridge that can run six or seven years, that flat payment loses real purchasing power.

When Payments Stop

The supplement ends at the end of the month before you turn 62, whether or not you claim Social Security at that point.¹⁰ Retirees who plan to delay Social Security to 65 or 70 for a larger monthly benefit need to plan for that gap; the supplement will not fill it.

The supplement also does not carry forward to survivors. If a recipient dies before 62, payments stop. A surviving spouse may qualify for a FERS survivor annuity, but the supplement is not part of that benefit.¹¹

1
eCFR. 5 CFR Part 842 Subpart E – Annuity Supplement
2
Office of the Law Revision Counsel. 5 USC 8421 – Annuity Supplement
3
Office of Personnel Management. CSRS and FERS Handbook – Chapter 51 Retiree Annuity Supplement
4
Office of Personnel Management. Information for FERS Annuitants RI 90-8
5
eCFR. 5 CFR 842.503 – Eligibility for Annuity Supplement
6
U.S. Office of Personnel Management. Eligibility
7
Office of Personnel Management. FAQs and Answers About the FERS Annuity Supplement Survey
8
Social Security Administration. Special Earnings Limit Rule
9
eCFR. 5 CFR Part 841 Subpart G – Cost-of-Living Adjustments
10
U.S. Office of Personnel Management. Will the FERS Annuity Supplement Continue After Age 62
11
U.S. Office of Personnel Management. Survivor Benefits