How do provisional income rules determine taxable Social Security in 2026?

1. What provisional income is and how it’s computed

Provisional income — sometimes called “combined income” in taxpayer guidance — equals adjusted gross income plus tax‑exempt interest plus one‑half of Social Security benefits; that sum is the IRS trigger for whether any benefits enter taxable income ^{[1] [4] [5]}. The routine worksheet used by tax preparers and IRS Publication 915 starts with regular taxable income, adds tax‑exempt interest, and then adds 50% of the SSA‑1099 benefit amount to reach provisional income ^{[1] [5]}.

2. The two threshold tiers that determine taxation in 2026

Two statutory provisional‑income thresholds set the tax buckets: for single, head‑of‑household, or qualifying widow(er) filers the lower threshold is $25,000 and the upper threshold is $34,000, while married filing jointly uses $32,000 and $44,000; taxpayers below the lower threshold generally owe no federal tax on Social Security benefits ^{[2] [5]}. Married filing separately who lived with their spouse during the year face a special rule that effectively causes up to 85% of benefits to be taxable because their threshold is treated as zero for the usual two‑tier test ^[2].

3. How much becomes taxable once thresholds are passed

If provisional income falls between the lower and upper thresholds, up to 50% of benefits may be included; once provisional income exceeds the upper threshold, the inclusion ramps up and the law limits the taxable amount to the lesser of two calculations — generally either 85% of benefits or a formula that adds 85% of the excess provisional income above the second threshold to a smaller statutory amount — so practical taxable portions are capped at 85% ^{[2] [1]}. The Congressional Research Service summarizes this statutory “lesser of” rule and the statutory dollar components that feed the phase‑in formulas used for 2026 ^[2].

4. Temporary senior deduction and legislative uncertainty

P.L. 119‑21 created a temporary “senior bonus” deduction — up to $6,000 (or $12,000 married filing jointly) for eligible taxpayers 65+ — that applies through 2028 and can reduce a retiree’s provisional income and therefore the chance of benefits being taxed in 2026 ^[3]. At the same time, proposals like the You Earned It, You Keep It Act could eliminate federal taxation of Social Security beginning with 2026 tax returns if passed, but as of early 2026 those proposals remained pending and therefore have not altered the statutory provisional‑income rules ^[3].

5. State taxes and other practical considerations

Nine states still tax Social Security in 2026, with widely varying age and income exemptions, so a retiree’s final state tax bill depends on state rules as well as the federal provisional‑income outcome ^{[6] [3]}. Tax planning matters because actions that raise AGI — such as Roth conversions or larger retirement account withdrawals — increase provisional income and can push someone past the thresholds; conversely, qualified charitable distributions and the senior deduction can lower provisional income and protect benefits from federal taxation ^{[6] [7]}.

6. What taxpayers should take away

For tax year 2026 the mechanics are clear: compute provisional income (AGI + tax‑exempt interest + ½ Social Security), compare it to the two statutory thresholds, and then apply the statutory formulas that cap inclusion at 85% — while remembering that the temporary senior deduction and state rules can materially change outcomes for many retirees ^{[1] [2] [3]}. Reporting and advisory sources recommend simulating provisional income under likely scenarios before making withdrawals or conversions because small changes in AGI can trigger a much larger tax bite when provisional income crosses the statutory thresholds ^{[8] [7]}.