US · Disability benefits

SSDI back pay calculator.

Enter your monthly SSDI benefit, your disability onset date, the date you applied and the approval date. You get the months owed, the gross back pay, the attorney fee under the standard fee agreement, and what is left. It runs in your browser; nothing you type is sent or saved.

Estimate only. Rules as published by SSA; fee cap as of the May 6, 2025 Federal Register notice.

Inputs

Result

Fill in the four fields and press Calculate.

How SSDI back pay is worked out

Back pay (SSA calls it past-due benefits) is every month you were entitled to SSDI but had not yet been paid when you were approved. The calculator finds the first month you are owed, the last month, and multiplies the months by your monthly benefit.

The steps

Waiting period. Five full calendar months of disability must pass before entitlement can begin. If onset is the 1st of a month, that month is the first of the five. If onset is any later day, the wait starts on the 1st of the next month. The first month you can be entitled is the sixth. With the ALS box ticked there is no wait.
Retroactivity limit. Benefits can reach back at most 12 months before the month you applied. The first month owed is the later of (a) the first month after the waiting period and (b) the application month minus 12.
Last month counted. Past-due benefits run through the month before the month of the approval decision. Benefits for the decision month onward are ongoing benefits, not back pay.
Months owed = last month − first month + 1 (never below zero). Gross back pay = months owed × monthly benefit.
Attorney fee = the lesser of 25% of gross back pay or $9,200. Net = gross − fee.
Payment timing. A month’s benefit is paid in the following month, so the first month owed is paid starting the month after. The tool shows that month, not a delivery date.

Worked example

Onset January 1, 2024, application March 10, 2024, approval December 5, 2024, benefit $1,000. The waiting period covers January to May 2024, so entitlement starts June 2024. The 12-month limit reaches back to March 2023, which is earlier, so the waiting period decides. The last month counted is November 2024. That is 6 months, $6,000 gross, a $1,500 fee (25%), and $4,500 net. Press “Try an example” for a case that hits the 12-month limit and the fee cap.

Limits of this tool

It assumes one fixed monthly amount. It does not apply annual cost-of-living increases, offsets (workers’ compensation, public disability benefits), SSI reimbursement, family benefits or Medicare.
It uses the onset date you enter. SSA decides the established onset date.
The fee cap applies to standard fee agreements. Fee petitions can differ. SSA’s user fee is charged to the representative and is not modelled. The $9,200 figure is as of the May 6, 2025 notice; SSA can raise it, so confirm the current cap.
It is not legal advice and does not predict whether a claim will be approved.

Sources

SSA POMS DI 25501.300, Waiting period: secure.ssa.gov/poms.nsf/lnx/0425501300
SSA POMS DI 10105.070, DIB entitlement and retroactivity: secure.ssa.gov/poms.nsf/lnx/0410105070
20 CFR 404.315, Who is entitled to disability benefits: law.cornell.edu/cfr/text/20/404.315
20 CFR 404.621, Retroactive entitlement (up to 12 months for disability): law.cornell.edu/cfr/text/20/404.621
20 CFR 404.1703, Definition of past-due benefits: law.cornell.edu/cfr/text/20/404.1703
Federal Register, Maximum Dollar Limit in the Fee Agreement Process ($9,200 effective November 30, 2024): 2024-10248; partial rescission, $9,200 remains in effect (May 6, 2025): 2025-07813

Cite this page: TNAADO Tools, “SSDI Back Pay Calculator,” tools.tnaado.ca/calculators/general/ssdi-back-pay-calculator/.

SSDI back pay FAQ

How is SSDI back pay calculated?

Back pay is the monthly benefit multiplied by the number of months you were entitled but not yet paid. Entitlement starts after a five-full-calendar-month waiting period that begins with your established onset date, but it can reach back no more than 12 months before the month you applied. Months are counted up to, but not including, the month of the approval decision.

Why is there a five-month waiting period?

SSDI does not pay for the first five full calendar months of disability. If your established onset is the 1st of a month, that month is the first month of the wait. If it is any later day, the wait starts the 1st of the next month. Benefits can begin with the sixth full month. The only exception this calculator handles is ALS, which has no waiting period for awards with a notice date on or after July 23, 2020.

How far back can SSDI back pay go?

Up to 12 months before the month you applied, and never before the waiting period ends. If your onset was years earlier than your application, the 12-month limit is what usually decides the start month. Together with the five-month wait, the earliest month counted can be 17 months before the application month.

When do I actually receive back pay, and is it one payment?

Social Security pays a month's benefit in the following month, and past-due benefits are usually paid as a lump sum after approval, though SSA may pay large amounts in installments. The calculator shows the first month a payment would cover. It does not predict the date a check arrives, because processing time varies.

How much can the attorney take from my back pay?

Under a standard fee agreement the representative's fee is 25% of your past-due benefits or $9,200, whichever is lower. SSA withholds that amount from the back pay and pays it directly. SSA also charges the representative a user fee, which is not taken from you. Fee petitions and other arrangements can differ. The cap is a dollar figure SSA can raise, so check the current amount with SSA.

Why might my real back pay be different from this estimate?

This tool assumes one fixed monthly amount. Real awards can include annual cost-of-living increases, offsets such as workers' compensation or public disability benefits, the SSI reimbursement rules, family-member benefits, and Medicare effects. A different onset date than the one you claimed will also change the result. Use it as a planning figure, not a decision or award notice.

What this calculates, and what it does not

This is an estimate from the dates and amount you enter and the published SSA rules above. It is not an award notice, legal advice or a prediction of approval. Only SSA decides your onset date, entitlement and payment.