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. (The period ends “at the end of the twelfth month beginning on or after” the start date, so an annuity that starts after the 1st of a month gets the rest of that month plus 12 more at 60 percent.) 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. Some people skip the phases entirely; see the question on when there is no 60/40 phase.

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 (1.7 percent for up to 20 years of law enforcement, firefighter, air traffic controller or other special-provision service), and pays that if it beats the 60 or 40 percent figure after the SSDI offset. Deposited military service counts toward the years. 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) if you were on the disability rolls the day before your 62nd birthday. That includes people who never had a 60/40 phase because they already met an immediate-retirement test. Your creditable service, including deposited military 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 (always 1 percent if you retire while still in a law enforcement, firefighter, air traffic controller or other covered position), with special-provision service credited at 1.7 percent. If you retire while serving in the covered position, your time on the rolls is credited as covered service at 1.7 percent too, until covered service and rolls time together reach 20 years. OPM Benefits Administration Letter 10-105: "if the employee retired while serving as a law enforcement officer, firefighter, nuclear materials courier, member of the Capitol Police, or member of the Supreme Court Police, the additional time during which the individual received disability annuity that is credited in the recalculation will also be subject to the 1.7 percent annuity accrual rate in § 8415(d), subject to the 20 year limitation" (the same applies to CBP officers). If you left the covered position before you separated, rolls time is at the ordinary rate. The SSDI offset stops. 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. Cost-of-living increases do not close that gap: the 40 percent annuity receives them from month 13 on, so indexing lifts both figures by roughly the same amount. An SSDI offset works the other way, because it lowers the 40 percent figure and so makes a rise at 62 more likely. 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 are already 62 (OPM counts you as reaching an age on the day before your birthday, OPM Handbook chapter 46, so an annuity starting the day before your 62nd birthday starts at 62) or 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, age 62 with 5, or, for law enforcement officers, firefighters, CBP officers, nuclear materials couriers, Capitol and Supreme Court Police and air traffic controllers, 25 years of that service at any age or age 50 with 20 (sections 8412(d) and (e)). MRA+10 is subsection (g) and is expressly excluded, so MRA+10 eligibility alone keeps you in the 60/40 branch. If the annuity starts before 62, it is still recomputed at 62.

When does OPM count me as 62, or 60, or 50?

On the day before the birthday. OPM CSRS/FERS Handbook chapter 46: "For retirement purposes, an employee is considered to reach a year of age on the day before his or her birthday". A disability annuity starts the day after you separate (5 CFR 844.301), so if it starts on your 62nd birthday you separated at 62, and with 20 years of service the earned annuity uses the 1.1 percent factor. The same rule applies to the age 60, minimum retirement age and special-provision age 50 tests. The age-62 recomputation itself takes effect on your 62nd birthday (5 CFR 844.305).

How does part-time service change a FERS disability annuity?

It depends on the phase. The earned annuity and the age-62 recomputation are computed "under section 8415" (5 U.S.C. 8452(b)(2)(A), (c), (d)(1)), so 8415(g)(1) applies: the annuity is computed on the full-time rate of pay and then multiplied by the ratio of your actual service to full-time service, which OPM rounds to the nearest percent. Twenty years at 62 with the first ten at half time gives a factor of 0.75, so a $100,000 high-3 earns $16,500 a year rather than $22,000. The 60 and 40 percent phases are not prorated; OPM computes them on a high-3 built from the pay you actually received (Handbook ch. 55, 55B2.1-1). Enter your part-time time and weekly hours and the calculator prorates the 8415 figures.

Does this calculator work for Congressional staff, dual-status technicians or someone who was on workers' compensation?

Not for the 8415-based figures. A Congressional employee with at least 5 years of Congressional or Member service has up to 20 of those years computed at 1.7 percent under 5 U.S.C. 8415(c), unless a revised or further revised annuity employee (8415(d)); Members have their own formula in 8415(b). 8415(i)(2) says the 1.1 percent factor "does not apply in the case of a Congressional employee, military technician (dual status), law enforcement officer" and other covered groups. Time credited while receiving OWCP compensation earns 1 percentage point more under 8415(n) once it reaches 2 months. The tool does none of this; tick the box that applies and the result is flagged as not reliable.

How much service do I need to qualify?

Only 18 months of creditable civilian service, under 5 U.S.C. 8451(a)(1)(A). Military service does not count toward the 18 months, although deposited military service does count when the annuity is computed. 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, OPM Handbook ch. 55 (part-time) · Inputs stay in your browser. Nothing you type is sent anywhere.

Your numbers

Date of birthSets the age-62 recomputation date. OPM counts you as reaching an age on the day before your birthday.

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

Civilian service only, including any special-provision years. You need at least 18 months of it to qualify at all.

Military service, deposit paid (optional)

Counts in the earned annuity and the age-62 recomputation, not toward the 18 months. Leave blank if the deposit is unpaid or you draw military retired pay for it.

Special-provision service (optional)

The part of your civilian service as a law enforcement officer, firefighter, CBP officer, nuclear materials courier, Capitol or Supreme Court Police, or air traffic controller. Credited at 1.7 percent, and 20 years at 50 (or 25 at any age) removes the 60/40 phases.

Part-time service (optional: years, months, hours a week)

Leave blank if every year was full-time. Part of the civilian service above. Enter the high-3 at the full-time rate. The earned annuity and the age-62 figure are multiplied by your actual-to-full-time service ratio (5 U.S.C. 8415(g)).

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, percentIndexes your high-3 for the age-62 recomputation and, at the same rate, the 40 percent phase it replaces, so the change at 62 compares like with like. Set it to 0 to match OPM's own examples.

Who this does not fit

Congressional employees and Members have their own 1.7 percent formula (5 U.S.C. 8415(b)-(d)); they and dual-status military technicians are barred from the 1.1 percent factor (8415(i)(2)); time credited while on workers' compensation earns an extra 1 percent (8415(n)). Front-line air traffic controllers with 5 or more years have that service credited at 1.7 percent with no 20-year limit (OPM BAL 10-105). None of that is in this tool. Tick what applies and the result will flag it.

Some of my service was as a Congressional employee or Member of Congress.I am a military technician (dual status).Some of my service credit is for time I received OWCP workers’ compensation.My special-provision service is air traffic controller service.

Your disability annuity

$2,600 a month to start

$2,600 a month for the rest of June 2026 plus the next 12 months (through June 30, 2027), then $1,853 a month (in starting dollars; with your assumed 2.0 percent increases it reaches $2,397 just before 62) for 153 months until age 62, then $3,060 a month after the age-62 recomputation - a rise of $663 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. The first two rows are in starting dollars; the age-62 row includes your assumed increases.
Phase	Rate	SSDI offset	Formula result	Payable
Through June 30, 2027 (partial first month + 12)	60 percent of high-3	$21,600/yr	$2,600	$2,600
Month 13 to age 62 (153 months)	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	$3,060	$3,060

At 62 the annuity rises by $663 a month.

Measured against the $2,397 a month the 40 percent phase pays just before 62, after the same assumed cost-of-living increases. The recomputation credits your time on the annuity rolls as service and indexes your high-3, but it also ends the 40 percent rate. 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, which is the day before the annuity starts (5 U.S.C. 8415(i)(2)(B); 5 CFR 844.301). OPM counts you as reaching 62 on the day before your 62nd birthday (OPM Handbook ch. 46).

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

Through June 30, 2027 (partial first month + 12)

$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 (153 months)

$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

Shown in starting dollars. Cost-of-living increases are payable from here, even though you are under 62, and the SSDI amount offset rises with them (5 U.S.C. 8452(a)(1)(B)(ii), (a)(2)(B)(i)(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 at each of the 14 December 1 cost-of-living adjustments falling between June 30, 2026 and your redetermination date: $88,000 becomes $116,114.13 (5 U.S.C. 8452(b)(2)(B)(ii); adjustments are effective December 1 under 8462(b)(1)).
$116,114.13 x 28 years 9 months x 1.1 percent = $36,721.09 a year
divided by 12 and rounded down = $3,060 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.
Compared with what the 40 percent phase pays just before 62 in the same dollars: $2,397 a month after 13 cost-of-living adjustments at your assumed rate (5 U.S.C. 8452(a)(1)(B)(ii)).

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 60 percent period (the rest of June 2026 plus the next 12 months (through June 30, 2027)). 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 — including the case where age 62 arrives first. 5 U.S.C. 8452(a)(1)(A) is expressly subject to subsection (b), and 8452(b)(1) makes the redetermined annuity payable "in lieu of" the disability rate from the 62nd anniversary, so a 60 percent period can be cut short and the 40 percent phase can never begin at all.	Indexing of the 40 percent annuity and the assumed SSDI benefit in the phase table itself: those rows are in starting dollars. Both are indexed at your assumed rate (5 U.S.C. 8452(a)(1)(B)(ii), (a)(2)(B)(i)(II)) only for the just-before-62 figure the age-62 change is measured against.
The earned-annuity floor under 8452(d)(1), compared after the SSDI offset in both phases.	Cost-of-living indexing of the floor in the phase table. 8452(d)(2) indexes it from commencement; the tool applies that only to the just-before-62 comparison, at full rate, without the 8462(c) proration of the first increase.
The age-62 recomputation: time on the rolls credited as service, the high-3 indexed at each December 1 cost-of-living adjustment date that falls before your redetermination date (5 U.S.C. 8462(b)(1) makes adjustments effective December 1; 8452(b)(2)(B)(ii) indexes average pay by all of them, whether or not your annuity was affected), 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 December 1 dates are counted exactly, but the RATE at each one is the single figure you assume; real adjustments vary year to year and are capped by the 8462(b) FERS formula.
Special-provision service (law enforcement, firefighter, CBP officer, nuclear materials courier, Capitol and Supreme Court Police, air traffic controller): up to 20 years credited at 1.7 percent in the earned annuity and at 62 (5 U.S.C. 8415(e); OPM), and at 62, if you retire from the covered position, time on the rolls credited at 1.7 percent as well within the same 20-year limit (OPM Benefits Administration Letter 10-105), the rest at 1 percent once covered service reaches 20 years or whenever you are still in a covered position at separation (OPM Handbook ch. 54: the 1.1 percent formula "does not apply to individuals who, at the time of the separation on which retirement is based, are law enforcement officers, firefighters, or air traffic controllers"; 5 U.S.C. 8415(i)(2)), and the 8412(d)/(e) test (25 years, or 50 with 20) that removes the 60/40 phases under 8452(c)(2).	A worked OPM example for a mixed career that left the covered position before separating (the tool then uses 1.1 percent where service reaches 20 years, and says to confirm it with OPM). Mixing air traffic control with other covered service for the 8412 tests, and any CSRS component. Front-line air traffic controller service with at least 5 years is credited at 1.7 percent with no 20-year limit (OPM Benefits Administration Letter 10-105; 5 U.S.C. 8415(f)); the tool keeps the 20-year limit, and if you tick the air traffic controller box the result warns you when that limit binds.
Military service with the deposit paid, counted in every 8415 computation and in the 8412 age-and-service tests, but not toward the 18 civilian months (8451(a)(1)(A); 8411(c)).	Whether your deposit is paid, and the bar on crediting military service you receive retired pay for. Enter only service that will count.
The 1.1 percent factor at separation tested on the day before the annuity starts (5 CFR 844.301; 8415(i)(2)(B)), with every age reached on the day before the birthday as OPM counts it (Handbook ch. 46), and no age-62 redetermination for an annuity that starts on or after the 62nd birthday (8452(b)(1)).	A commencing date set by the day pay ceases rather than the day after separation. Enter the date your annuity actually starts.
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 civilian service floor, and the 8452(c) branch where there is no 60/40 phase at all, including its age-62 redetermination when the annuity starts before 62.	Whether OPM will approve the disability itself, the agency accommodation and reassignment search, and the SSDI application requirement.
Part-time service in the earned annuity and the age-62 recomputation: computed on the full-time high-3, then multiplied by the ratio of actual to full-time service rounded to the nearest percent (5 U.S.C. 8415(g)(1); OPM Handbook ch. 55, 55B2.1-1). Time on the rolls enters the age-62 factor as full-time.	The 60 and 40 percent phases for someone whose high-3 years include part-time pay: OPM uses actual (prorated) pay rates there and no proration factor (Handbook ch. 55, 55B2.1-1(E) note); the tool uses the one full-time high-3 and warns. Intermittent service (8415(g)(2)) and part-time VHA title 38 service (Handbook ch. 55, 55B4).
Regular FERS service at 1 or 1.1 percent in every 8415 computation.	Congressional employees and Members. 5 U.S.C. 8415(c): with at least 5 years of Congressional or Member service, that service "not exceeding a total of 20 years, shall be computed by multiplying 1 7/10 percent of the individual's average pay by the years of such service"; 8415(b) is the Member formula; 8415(d) returns revised and further revised annuity employees to the regular formula; 8415(i)(2) bars them from 1.1 percent. A ticked box flags the result as not reliable.
The 1.1 percent factor at 62 with 20 years for regular employees.	Military technicians (dual status). 5 U.S.C. 8415(i)(2): the 1.1 percent rule "does not apply in the case of a Congressional employee, military technician (dual status), law enforcement officer, ...". The tool may show 1.1 percent where a dual-status technician gets 1 percent; a ticked box flags the result.
Every credited month at the same percentage.	Workers' compensation (OWCP) credit. 5 U.S.C. 8415(n): with "at least 2 months of credit under section 8411(d) for any period while receiving benefits under subchapter I of chapter 81, the percentage otherwise applicable ... for that period so credited shall be increased by 1 percentage point." That reaches the earned annuity and the age-62 recomputation (8452(b)(2)(A), (c), (d)(1)). The tool understates them; a ticked box flags the result.
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 (plus the rest of the first month, if the annuity starts after the 1st), 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. If you already meet an immediate-retirement test when the annuity starts (including the law enforcement and firefighter 50-with-20 test), there are only two numbers: the earned annuity, then the age-62 recomputation.

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. That softens the drop from 60 percent to 40 percent, but it does not usually reverse it. Combined FERS plus SSDI income in year two is 40 percent of your high-3 plus 40 percent of your SSDI, so it exceeds the year-one figure only when your annual SSDI is more than half your high-3. On the example above it falls.

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, with special-provision years (and, if you retire from the covered position, time on the rolls, up to 20 years in all) at 1.7 percent. The calculator compares the two in the same dollars: the age-62 figure against what the 40 percent phase pays just before 62 after the same assumed increases.

With no SSDI offset, the break-even is about 36 years of adjusted service (40 percent divided by 1.1 percent is 36.4). Cost-of-living increases barely move it, because the 40 percent annuity receives them too; an SSDI offset lowers it. 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. Military service does not count toward it, though deposited military service does count in the computation. 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.