Retirees who receive a retroactive Social Security payment can ask the IRS to figure the tax on the back benefits as if they had arrived in the earlier years they cover. The election, laid out in Publication 915, applies when a lump sum includes benefits for a prior year, and the IRS says it can be used if it lowers the taxable benefits. The tax still lands on the return for the year the money arrived.
Back pay builds up when a claim takes months to approve, or when an award reaches back to an earlier month of eligibility. Without the election, the whole payment goes into one year’s income test, where it can lift a retiree over the base amount or push more of the benefit into the 85% tier.
How the earlier-year election works
Section 86(e) of the tax code lets a taxpayer limit the amount included this year to the sum of the increases in gross income that would result if the back portions were counted in the years they belong to. A benefit belongs to a year if its generally applicable payment date fell in that year. The election is made as the IRS prescribes.
Publication 915 turns this into worksheets. Worksheet 2 handles a lump sum for a year after 1993, and Worksheet 3 handles 1993 or earlier, and both feed Worksheet 4. A separate Worksheet 2 or 3 is completed for each earlier year the payment covers, which means old returns have to come out of the drawer.
Each earlier year needs that year’s income, because the worksheet asks what the tax would have been then. The filer checks a box on line 6c of the Form 1040 or 1040-SR, and the publication says plainly, “Don’t file an amended return for the earlier year.” The earlier return stays as filed, and the result is reported on the return for the year the money arrived.
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When the election pays off
A simplified case with no other benefits shows the pattern. A single retiree receives $8,000 of back benefits for the prior year, when other income was $15,000, and has $30,000 of other income in the year of payment. Counted in the payment year, half the benefit plus other income comes to $34,000, which is $9,000 over the $25,000 base, so the full $4,000 half of the benefit is taxable.
Counted in the earlier year, the same back pay produces $19,000 of combined income, under the base, and no taxable benefit. The election removes $4,000 of taxable income from the payment year. For a filer in the 22% bracket, that is $880 of federal tax.
Retirees with the opposite pattern may find the regular method cheaper. A retiree who earned less in the payment year than in the earlier years, perhaps after leaving a job, can end up with more taxable benefit under the election. That is why Publication 915 says retirees can elect the method “if it lowers your taxable benefits.”
Whether the choice is worth making depends on the numbers for each year. Retirees who see back pay of several thousand dollars should run both versions before filing. Worksheets 2 or 3 and Worksheet 4 produce the election figure, and the ordinary Worksheet 1 or A produces the regular one, so the two can sit side by side before anything is filed.
Locking in the choice
The decision is hard to undo. Publication 915 says the election can be revoked only with the consent of the IRS, and the statute says the same. A retiree who checks the box and later finds a mistake in an old year’s figures needs the agency’s permission to switch back.
IRS Topic 423 points anyone who “received benefits in the current tax year that were for a prior year” to the Publication 915 election, and says Form SSA-1099 arrives by early February for the prior calendar year. The form reports benefits paid in box 3, benefits repaid in box 4 and net benefits in box 5.
The choice comes at filing time, after the SSA-1099 arrives, not when the money is deposited. Retirees who want tax taken out of benefits during the year can file Form W-4V, “Voluntary Withholding Request,” which the same topic page describes. A lump sum is the kind of payment where withholding is worth asking about.
Any repayment is handled first. Publication 915 says repayments of benefits made during the year are subtracted from the gross benefits received, which changes the starting figure before the election is considered. A retiree who got back pay and also repaid an overpayment in the same year does both calculations on the same return.
For retirees who qualify, the election is the difference between taxing a long wait at the rates of the year of payment and taxing it at the lower rates of the years it was earned. The worksheets are free in the publication, and the only cost is the hour it takes to run them for each earlier year.
Waiting on Social Security back pay?
A lump sum of back benefits can be taxed two ways on the same return, and the difference can run to hundreds of dollars. Picking the wrong way, or never knowing there was a choice, leaves that money with the IRS.
Cut Your Retirement Tax Bill: 12 Moves covers the income lines behind that choice, including how much of your Social Security is taxed, worked out on one worksheet, and the 2026 numbers on one page. It pairs each of the 12 moves with the form to use, among them Form W-4V, the form for withholding tax from benefits.
Get the 12-move tax kit with the one-worksheet Social Security tax walkthrough →
This article was produced with AI assistance and edited for accuracy against the sources linked above.
