SSDI Back Pay Calculator

1. Find the established onset date (EOD), the date SSA decides your disability began.
2. Add the five full calendar month waiting period. Benefits start with the sixth full month.
3. Do not go back further than 12 months before the month you applied.
4. End with the month before the month SSA processes (effectuates) the award.
5. Add each month at that month's benefit amount, with COLAs, rounded down as SSA rounds.

Worked example. Your onset date is January 15, 2025, you apply in March 2025, and SSA processes the award in October 2026. Your benefit is $1,500 a month for payments made in 2026.

• Onset is after the 1st, so the waiting period starts February 1: February through June 2025. Entitlement is July 2025.
• The 12-month limit reaches back to March 2024, earlier than July 2025, so it does not apply. Back pay starts July 2025.
• Back pay ends September 2026, the month before the October 2026 processing month. That is 15 months.
• Benefit months through November 2025 are paid in 2025 at the 2025 amount ($1,459, backed out of $1,500 by the 2.8% COLA, the 2026 COLA), 5 months, $7,295. Benefit months from December 2025 are paid from January 2026 at $1,500, 10 months, $15,000.
• Back pay: $22,295. The October 2026 benefit is the first regular payment, paid in November 2026.
• With a representative on a fee agreement, the fee is the lesser of 25% ($5,573.75) and $9,200: $5,573.75, leaving $16,721.25.

Month of entitlement versus month of payment

Social Security pays benefits the month after the month they are for (SSA Handbook section 121). The COLA effective in December is for the December benefit, which is paid in January, so SSA's “2027 COLA” of 3.6% (named for the year it is first paid) raises the December 2026 benefit, paid in January 2027. The calculator lists both the benefit month and the month it is paid. See the Social Security COLA 2027 page for the current increase.

How SSA rounds

Each COLA raises your benefit and SSA lowers the result to the next lower 10 cents (42 U.S.C. 415(i)); the amount paid is lowered to the next lower dollar (42 U.S.C. 415(g); 20 CFR 404.304(f)). A $1,500 benefit with the 3.2% (2024 COLA), 2.5% (2025 COLA) and 2.8% (2026 COLA) increases becomes $1,548.00, then $1,586.70 (paid as $1,586), then $1,631.10 (paid as $1,631).

The waiting period. You must be disabled for five full calendar months in a row before benefits begin (42 U.S.C. 423(c)(2); 20 CFR 404.315(a)(4)). If your onset date is the 1st of a month, that month counts: an onset of June 1 means June through October, and benefits start in November. If your onset is any later day, the count starts the next month: an onset of June 15 means July through November, and benefits start in December (POMS DI 25501.300; SSA Office of the Inspector General audit 072304).

The retroactivity limit. If you apply after you could have been entitled, benefits can start up to 12 months before the month you applied (20 CFR 404.621(a)(1)). SSA also begins the waiting period no earlier than the 17th month before the month you apply, which gives the same result: the earliest possible entitlement is 12 months before your application month.

No waiting period. ALS claims approved on or after July 23, 2020 have none, and neither do claims where the new onset falls within five years of the end of an earlier disability entitlement (20 CFR 404.315(a)(4); POMS DI 10105.075). Benefits then begin with the first full month of disability, still limited to 12 months before you applied.

No dollar figure caps SSDI back pay. The most you can be owed is set by time and by your benefit: up to 12 months before your application, plus every month until SSA processes the award. A claim that takes two years at the hearing level can produce a far larger lump sum than one approved in months. Your benefit amount is based on your lifetime earnings, so the larger your benefit, the larger the same number of months is worth.

Retroactive months are the months before your application month, up to 12. Back pay (SSA calls it past-due benefits) is every month owed before the first regular payment: the retroactive months plus the months that pass while the claim is pending, from your first benefit month through the month before the first regular payment. The waiting period months are never paid. The calculator counts that whole span.

• No retroactive SSI. SSI is paid from the month after you apply, if you meet every other requirement that month (20 CFR 416.335). SSA counts SSI past-due benefits through the month it processes the award (POMS GN 03920.031).
• Installments. If the past-due SSI, after interim assistance repayment, a direct representative fee and withheld overpayments, equals or exceeds three times the monthly federal benefit rate, SSA pays it in up to three installments six months apart. Each of the first two is limited to three times the rate: $2,982 in 2026 ($994 x 3). The third is the balance. You can ask for more up front for certain debts, medical needs and housing costs. Installments do not apply if death is expected within 12 months or you are no longer eligible and likely to stay that way for 12 months (POMS SI 02101.020; 42 U.S.C. 1383(a)(10)).
• Both SSI and SSDI. You can be awarded both, but SSA reduces retroactive SSDI by SSI it paid for the same months that it would not have paid had SSDI come on time (20 CFR 404.408b). The offset can come out of either the SSDI or the SSI payment (POMS GN 03920.031 B.2). This calculator does not compute it; it shows how many SSI months overlap your SSDI back pay and estimates installments only for the SSI months outside that overlap. After the award, SSI is reduced by your SSDI as income, often to zero if your SSDI is above the federal rate.

Under a fee agreement approved by SSA, the representative's fee is the lesser of 25% of past-due benefits or a dollar cap (42 U.S.C. 406(a)). The cap is $9,200 for favorable decisions on or after November 30, 2024, up from $7,200 (November 30, 2022 to November 29, 2024); SSA has said it will publish a Federal Register notice only when it raises the cap again (90 FR 19241, May 6, 2025: “the $9,200 fee cap will remain in effect”; POMS GN 03920.006). The cap is set by the date of the favorable decision, and if your agreement names a lower amount, SSA authorizes only that amount. This page uses the processing month you enter as a stand-in for the decision date. Past-due benefits for the fee run through the month before the month SSA processes the award (POMS GN 03920.030 B.1; 20 CFR 404.1703 words it as up to but not including the month of the decision). SSA calls this “past-due benefits”, which is not the same as the “past-due benefits payable” after offsets and deductions. SSA withholds up to 25% of past-due benefits to pay the fee directly.

SSA charges the representative a user fee for direct payment: the lesser of 6.3% of the fee (the rate for 2026, 90 FR 57516; it is set each year) or a dollar cap, $123 for payments on or after December 1, 2025 and $120 from December 1, 2024. SSA applies the cap in effect when it pays, so this page uses the processing month as the payment date. It is taken from the representative's payment and cannot be charged to you (POMS GN 03920.019). SSA adjusts this cap each December with the COLA and had not published the December 1, 2026 figure when this page was checked, so approval months after November 2026 are not calculated. Fee petitions, which can produce a different fee, are not modeled.

Past-due SSDI is reported in the year you receive it, though part of it was owed for earlier years. The IRS lump-sum election lets you refigure the taxable part using those earlier years' income and use whichever method gives the lower taxable amount (IRS Publication 915). SSI is not taxable. To see how much of your benefits could be taxed, use the taxable Social Security benefits calculator. To compare claiming ages for retirement benefits, see the Social Security break-even calculator.

These can change your real back pay. Nothing below is approximated; your notice of award has the real figures.

• Workers' compensation and public disability benefit offsets.
• Auxiliary (family) benefits for a spouse or children, and the family maximum.
• Medicare Part B premiums deducted from benefits once Medicare starts, normally 24 months after entitlement (ALS: from the first month of entitlement). Past-due months after that point are paid net of the premium.
• Insured status and your date last insured: the waiting period must begin in a month you are insured for disability benefits.
• Conversion to retirement benefits at full retirement age, which ends disability benefits.
• Resource rules for the lump sum: unspent retroactive SSDI and SSI payments are excluded from SSI resources for 9 months after the month you receive them (20 CFR 416.1233).
• Overpayments, suspensions for work, trial work period, and closed periods of disability.
• The SSI windfall offset, SSI income and living-arrangement reductions, State supplements, and couples.
• Fee petitions, court fees, and fees on SSI past-due; the fee shown counts SSDI past-due only.
• Processing months before December 2024 or after November 2026, because the verified fee caps and published COLAs stop there.
• Your benefit amount: the calculator uses the figure you enter. It does not compute your PIA from earnings.