Updated August 7, 2026. Quick answer: take one more dollar out of an IRA in retirement and it can drag up to 85 cents of Social Security into taxable income alongside it. 🔴 So the tax on that dollar is far higher than your bracket says — and the thresholds that cause it have never been adjusted for inflation, not once since they were written.
How one dollar becomes almost two
Social Security is taxed on a test, not a rate. The statute compares a figure — your modified adjusted gross income plus one-half of your benefits — against two fixed thresholds, and the amount of benefit pulled into income rises as you cross them.
Above the upper threshold, the inclusion is driven by 85 percent of such excess, capped at “85 percent of the social security benefits received during the taxable year.”
🔴 That is the torpedo. Inside the range, an extra dollar of IRA withdrawal is itself taxable and makes up to 85 cents of previously untaxed benefit taxable. You are taxed on roughly $1.85 of income for taking out $1. The bracket did not change; the amount being taxed did.
⚠️ It ends. Once 85% of your benefits are already in income, the cap is reached and further withdrawals are taxed normally. The torpedo is a zone, not a permanent surcharge — which is exactly why where you land in it matters more than the size of any single withdrawal.
🔴 The numbers have never moved
The statute sets them as flat dollar amounts:
Base amount — $25,000, or $32,000 in the case of a joint return.
Adjusted base amount — $34,000, or $44,000 in the case of a joint return.
There is no indexing provision. These are hard numbers written into the Code, and unlike tax brackets, standard deductions or IRMAA tiers, nothing adjusts them each year.
⚠️ That single fact explains why this catches more people every year. Benefits rise with the annual cost-of-living adjustment; the thresholds do not move at all. A retiree who was below the line a decade ago can be above it now without a single decision having changed.
The version that starts at zero
The harshest provision in the section is one almost nobody mentions. For a taxpayer who is married at the end of the year, does not file jointly, and does not live apart from their spouse at all times during the year, both thresholds are:
zero
🔴 No exempt band at all. Benefits are exposed from the first dollar. Couples who file separately for an unrelated reason — a student-loan calculation, a medical-deduction threshold, a marital separation that has not become physical — can be handed this without anyone warning them. “Live apart at all times during the taxable year” is a demanding test, and it is the whole hinge.
The interest you bought to be tax-free counts anyway
The income figure used in the test is not plain AGI. It is adjusted gross income:
…increased by the amount of interest received or accrued by the taxpayer during the taxable year which is exempt from tax.
Municipal bond interest is exempt from tax and still counted here. A portfolio moved into munis specifically to reduce taxable income does nothing for this test — it can even be the reason someone is above the threshold while believing they are below it.
What actually helps
Know which zone you are in before December. The question is not “what is my bracket” but “is my next dollar dragging benefits in with it” — and the answer changes the case for taking income this year versus next.
Consider whether a large withdrawal is better split across two tax years or deliberately concentrated into one. Both can be right: splitting keeps you low in the zone twice; concentrating can push you past the 85% cap once and leave the following year clean. Which is better is arithmetic on your own numbers, not a rule.
Remember the RMD removes the choice. Once required distributions begin, the withdrawal is no longer optional, which is why the planning years are the ones before them: withdrawal order and the IRMAA brackets covers the neighbouring cliff, and it is a different test with different thresholds.
⚠️ Scope
No effective tax rate is asserted on this page. The multiplier depends on your bracket, your benefit size and where you sit in the range, and a headline percentage would be wrong for most readers. This is not tax advice, and it does not tell you whether to withdraw, convert or wait.
Sources
Quoted from 26 U.S.C. § 86 (social security and tier 1 railroad retirement benefits) — subsection (a)(2) (the 85 percent computation), (b)(2) (modified adjusted gross income, including exempt interest), and (c) (base amount and adjusted base amount) — via Cornell’s Legal Information Institute, retrieved 7 August 2026: law.cornell.edu. The threshold figures above are the statutory amounts themselves, which is why they carry no year label — there is no annual adjustment to label.