How is a FERS disability annuity calculated?

In two phases, under 5 U.S.C. 8452(a)(1). For the first 12 months you get 60 percent of your high-3 average salary, reduced by 100 percent of your SSDI benefit. After that, until age 62, you get 40 percent of your high-3, reduced by 60 percent of your SSDI benefit. In both phases you are paid your earned annuity instead if that is higher.

What is the earned annuity floor?

It is the protection in 5 U.S.C. 8452(d)(1): your annuity "shall not be less than the amount of an annuity computed under section 8415", excluding the MRA+10 age reduction. In other words, OPM works out the ordinary FERS pension you earned, 1 percent of your high-3 for each year of service, and pays that if it beats the 60 or 40 percent figure after the SSDI offset. For someone with long service, or a large SSDI award, the earned annuity is often the number that actually gets paid.

Which SSDI figure does OPM offset?

Not your current cheque. 5 U.S.C. 8452(a)(2)(B) defines the offset against your "assumed disability insurance benefit", which is the SSDI amount for the month your FERS annuity commences, then adjusted for later FERS cost-of-living increases. 5 CFR 844.302(a) calls the same figure the adjusted social security disability benefit. So enter the amount as of the month your annuity starts.

What happens at age 62?

OPM recomputes the annuity under 5 U.S.C. 8452(b). Your creditable service is increased by every period you were entitled to the disability annuity, and your high-3 is adjusted to reflect the cost-of-living increases that ran during that time. The factor is 1.1 percent if the adjusted service reaches 20 years, otherwise 1 percent. The SSDI offset stops. Be aware that the new figure replaces the old one with no protection against a decrease, so the annuity can go down at 62.

Why would my annuity fall at 62?

Because the 40 percent of high-3 floor disappears and is replaced by an ordinary service-based pension. For a mid-career employee, say someone retiring on disability at 48 with 15 years, the adjusted service at 62 is about 29 years, which at 1.1 percent is roughly 32 percent of high-3 rather than 40 percent. The cost-of-living indexing of the high-3 narrows the gap and can close it, but it does not always. 5 U.S.C. 8452(b)(1) makes the recomputed annuity payable "in lieu of" the old one, so there is no hold-harmless.

Do I get cost-of-living increases before 62?

Yes, after the first year. 5 U.S.C. 8452(a)(1)(B) blocks any adjustment during the 60 percent phase, then allows all of them afterwards. The usual rule that FERS retirees under 62 get no increases does not reach you, because 5 U.S.C. 8462(c)(3)(B)(i) applies that bar only to annuitants under sections 8412, 8413 and 8414, and a disability retiree comes under section 8451.

Is there ever no 60/40 phase at all?

Yes. Under 5 U.S.C. 8452(c) the annuity is computed the ordinary way under section 8415, with no phases, if it starts at or after your 62nd birthday, or if on the day it starts you already meet the age and service test for an immediate annuity under section 8412 other than subsection (g). That means MRA with 30 years, age 60 with 20, or age 62 with 5. MRA+10 is subsection (g) and is expressly excluded, so MRA+10 eligibility alone keeps you in the 60/40 branch.

How much service do I need to qualify?

Only 18 months of creditable civilian service, under 5 U.S.C. 8451(a)(1)(A). That is far lower than the 5 years needed for an ordinary FERS annuity, and it surprises most people. The harder test is the disability standard itself: OPM has to find you unable, because of disease or injury, to render useful and efficient service in your position.

Calculator

FERS Disability Retirement

A FERS disability annuity pays 60 percent of your high-3 for a year, then 40 percent until age 62, both reduced by any SSDI you receive, with your earned annuity as a floor. This works all three phases and shows what changes at 62, including when the number goes down.

Reviewed by Jonathan D., 20-year federal employee · Formulas verified against OPM.gov · Updated October 2026

Rule snapshot

Reviewed October 3, 2026 · Sources: 5 U.S.C. 8452, 5 CFR 844 subpart C, OPM Handbook ch. 61, OPM FERS computation · Inputs stay in your browser. Nothing you type is sent anywhere.

Your numbers

Date of birthSets the age-62 recomputation date.

Date the annuity startsUsually the day after your last day in pay status.

High-3 average salaryIf you have under 3 years of service, OPM averages your total service instead.

Creditable civilian service

You need at least 18 months to qualify at all.

SSDI benefit, monthly (optional)Use the amount for the month your annuity starts. Leave blank if you are not awarded SSDI. The law offsets that fixed figure, not your current cheque.

Survivor election

Assumed yearly increase, percentOnly used to index your high-3 for the age-62 recomputation. Set it to 0 to see the unindexed figure, which is what OPM uses in its own examples.

Your disability annuity

$2,600 a month to start

$2,600 a month for the first 12 months, then $1,853 a month until age 62, then $3,044 a month after the age-62 recomputation - a rise of $1,191 a month at 62.

The three phases

What is payable in each phase, after the SSDI offset and any survivor reduction, compared against your earned annuity.
Phase	Rate	SSDI offset	Formula result	Payable
First 12 months	60 percent of high-3	$21,600/yr	$2,600	$2,600
Month 13 to age 62	40 percent of high-3	$12,960/yr	$1,853	$1,853
From age 62April 10, 2040	1.1 percent x 28 years 9 months	Stops	$3,044	$3,044

At 62 the annuity rises by $1,191 a month.

The recomputation credits your time on the annuity rolls as service and indexes your high-3, but it also ends the 40 percent floor. There is no protection against a decrease: 5 U.S.C. 8452(b)(1) makes the new figure payable in lieu of the old one.

Your earned annuity (the floor under both phases)

$1,100 a month

$88,000 high-3 x 15 years of service x 1.0 percent = $13,200.00 a year
divided by 12 and rounded down = $1,100 a month
1 percent applies. The 1.1 percent factor needs you to be 62 or older with 20 or more years at separation (5 U.S.C. 8415(i)).

Under 5 U.S.C. 8452(d)(1) you are paid the greater of the phase formula and this figure, in both the 60 percent year and the 40 percent years. The comparison is made after the SSDI offset.

How we got this

First 12 months

$88,000 high-3 x 60 percent = $52,800.00 a year
less 100 percent of the $21,600.00 SSDI benefit ($21,600.00) = $31,200.00
divided by 12 and rounded down = $2,600 a month

No cost-of-living increase during this phase (5 U.S.C. 8452(a)(1)(B)(i)).

Month 13 to age 62

$88,000 high-3 x 40 percent = $35,200.00 a year
less 60 percent of the $21,600.00 SSDI benefit ($12,960.00) = $22,240.00
divided by 12 and rounded down = $1,853 a month

Cost-of-living increases are payable from here, even though you are under 62 (5 U.S.C. 8452(a)(1)(B)(ii); 8462(c)(3)(B)(i)).

Age-62 recomputation

Months credited for time on the rolls: 165 (13 years 9 months), counted to the day before your 62nd birthday (5 U.S.C. 8452(b)(2)(B)(i)).
Adjusted service: 15 years actual plus 13 years 9 months on the rolls = 28 years 9 months.
High-3 indexed by 2.0 percent a year over 13 years 9 months: $88,000 becomes $115,541 (5 U.S.C. 8452(b)(2)(B)(ii)).
$115,541 x 28 years 9 months x 1.1 percent = $36,539.75 a year
divided by 12 and rounded down = $3,044 a month
The 1.1 percent factor applies because adjusted service reaches 20 years.
The SSDI offset stops here. The redetermined annuity is computed purely under 5 U.S.C. 8415.

The SSDI figure the law offsets is your benefit for the month the annuity starts, indexed by later FERS cost-of-living increases. It is not your current cheque (5 U.S.C. 8452(a)(2)(B); 5 CFR 844.302(a)).
Your annuity receives no cost-of-living increase during the first 12 months. After that, a FERS disability annuitant does receive them even before age 62 (5 U.S.C. 8452(a)(1)(B); 5 U.S.C. 8462(c)(3)(B)(i)).
If you leave the disability rolls because OPM finds you recovered or restored to earning capacity, the time off the rolls is not credited as service and the cost-of-living increases in that gap do not raise your high-3 (OPM Handbook ch. 61, 61B2.1-3 D.2).
OPM must approve the disability itself. The standard is that you cannot render useful and efficient service in your position (5 U.S.C. 8451(a)(1)(B)).
Applying for SSDI is a condition of the FERS disability application. The offset only bites if SSDI is actually awarded.

What this models

The honest boundary of this tool. Anything in the right column changes your real number and is not in the math above.
Modeled	Not modeled
The 60 percent and 40 percent phases with the 100 percent and 60 percent SSDI offsets, floored at zero.	Indexing of the assumed SSDI benefit itself. The statute adjusts it by later cost-of-living increases; this tool holds it at the figure you enter.
The earned-annuity floor under 8452(d)(1), compared after the SSDI offset in both phases.	Cost-of-living indexing of the floor amount during the first year, which 8452(d)(2) requires and which can matter at the margin.
The age-62 recomputation: time on the rolls credited as service, the high-3 indexed by your assumed rate, and the 1 or 1.1 percent factor.	Any period you leave the rolls after a finding of recovery or restored earning capacity. That time is not credited and its increases do not raise your high-3.
The survivor reduction of 5 or 10 percent, applied after the SSDI offset as 5 CFR 844.302(d) requires.	Court-ordered apportionment, the alternative form of annuity, and FEHB or FEGLI premiums.
The 18-month service floor, and the 8452(c) branch where there is no 60/40 phase at all.	Whether OPM will approve the disability itself, the agency accommodation and reassignment search, and the SSDI application requirement.
Service in whole years and months.	Day-level service arithmetic. OPM adds years, months and days and carries 30 days into a month, so adjusted service at 62 can differ by one month.

Precision limits: service is handled in whole years and months, and the monthly figure is divided from the annual and rounded down to the dollar, which is the OPM convention. Future cost-of-living rates are unknowable, so the age-62 figure is only as good as the rate you assume. This is an estimate for planning, not an OPM determination.

Three numbers, not one

FERS disability retirement does not pay a single amount for life. It pays 60 percent of your high-3 for twelve months, then 40 percent until you turn 62, then an ordinary service-based pension after that. Each phase has its own SSDI offset, and each is subject to the earned-annuity floor.

Most write-ups cover the first two and skip the third. The third is the one that changes the plan, because for a lot of mid-career employees it pays less than the 40 percent it replaces.

The offset nobody explains properly

The law does not offset the SSDI cheque you happen to be receiving. 5 U.S.C. 8452(a)(2)(B) offsets your “assumed disability insurance benefit,” which is the SSDI amount for the month your FERS annuity started, then adjusted by later FERS cost-of-living increases. 5 CFR 844.302(a) uses the same construct.

There is also a quirk worth knowing: the offset is 100 percent in year one and only 60 percent afterwards. So if you receive SSDI, your combined income from FERS plus SSDI is usually higher in year two than in year one, even though the FERS share drops from 60 percent to 40 percent.

Why the annuity can fall at 62

At your 62nd birthday OPM recomputes under 5 U.S.C. 8452(b). The good part: every month you spent on the annuity rolls counts as service, and your high-3 is lifted by the cost-of-living increases that ran during that time. The hard part: the 40 percent floor is gone, replaced by 1 percent (or 1.1 percent at 20 or more adjusted years) of the indexed high-3 per year of service.

Run the arithmetic and the break-even is around 36 to 40 years of adjusted service. Many people land short of it. The statute is explicit that the new figure is payable “in lieu of” the old one, so there is no floor protecting you from the drop. The FERS Retirement Calculator is useful here for sanity-checking the post-62 figure against an ordinary retirement.

Eighteen months, not five years

The service requirement is 18 months of creditable civilian service (5 U.S.C. 8451(a)(1)(A)), far below the 5 years an ordinary FERS annuity needs. With under 3 years of service, OPM averages your total service instead of 3 consecutive years to get the high-3.

The real test is the disability standard: OPM has to find you unable, because of disease or injury, to render useful and efficient service in your position. That is a lower bar than the SSDI standard, which asks whether you can do any substantial gainful work anywhere in the economy. People are regularly approved for one and not the other.