Social Security benefits are subject to federal income tax once a retiree's income clears certain thresholds. Whether any of your benefit is taxed, and how much, is determined by a single figure the Internal Revenue Service calls combined income.
The rule sets three tiers and two sets of dollar thresholds, one for single filers and one for married couples filing jointly. What follows is the rule itself, how it applies as income rises, and the one input the rule leaves within your control.
Social Security taxation runs on a measure of income that appears nowhere else on your tax return. The IRS calls it combined income. It is also widely called provisional income. The two terms mean the same thing.
The formula: Combined income = your adjusted gross income (AGI) + any tax-exempt interest you earned + one half of your annual Social Security benefits.
Look closely at what counts and what does not. Combined income includes withdrawals from a traditional 401(k) or IRA, pension payments, wages, interest, dividends, and capital gains. It even includes tax-exempt interest from municipal bonds, which is otherwise invisible on your return. It includes only half of the Social Security benefit itself. And, as you will see below, it leaves out qualified Roth withdrawals completely.
Your combined income then lands in one of three bands. The band sets the share of your benefit that becomes taxable.
| Combined income (single) | Combined income (married, joint) | Share of benefit taxable |
|---|---|---|
| Under $25,000 | Under $32,000 | 0% |
| $25,000 to $34,000 | $32,000 to $44,000 | Up to 50% |
| Over $34,000 | Over $44,000 | Up to 85% |
Falling into the top band does not mean 85% of your benefit is taken in tax. It means up to 85 cents of every benefit dollar gets added to your ordinary taxable income. That income is then taxed at your regular marginal rate, which for most retirees is 10%, 12%, or 22%.
Consider a single retiree, owner A. She collects $24,000 a year in Social Security and withdraws $30,000 from a traditional IRA. Her combined income is $30,000 of IRA money plus $12,000, which is half of her benefit, for $42,000. That sits above the $34,000 single threshold, so a portion of her benefit, up to 85% of it, is included in her taxable income. The benefit pushes her taxable income up. It is not confiscated at 85 cents on the dollar.
The actual taxable portion comes out of a worksheet in the IRS instructions that fills the 50% and 85% bands gradually, so most people in the top band see something less than the full 85% taxed until their income climbs well past the threshold. The practical takeaway holds either way: more outside income means more of your benefit counts.
When Congress first made benefits taxable in 1983 and added the 85% tier in 1993, it set those dollar thresholds in statute and did not index them to inflation. The $25,000 and $32,000 figures are the same today as they were then.
Because the thresholds are frozen while incomes and benefits rise with inflation, the bands catch more people each year. When the tax began, fewer than one in ten beneficiaries owed anything on their benefits. Today the majority do. Nothing about a retiree's real standard of living has to change for them to drift from the 0% band into the taxable ones. The erosion is built into the design. Our guide on how inflation affects your plan covers the same drift on the spending side of the ledger.
The One Big Beautiful Bill Act, signed in July 2025, did not eliminate the tax on Social Security benefits, despite headlines to that effect. It created a separate deduction for older taxpayers that lowers the income on which those benefits are taxed.
The deduction is up to $6,000 per person age 65 or older, so up to $12,000 for a married couple where both spouses qualify. It is available whether you itemize or take the standard deduction. It phases out above $75,000 of modified adjusted gross income for single filers and $150,000 for joint filers, and disappears entirely at $175,000 and $250,000. It applies to tax years 2025 through 2028 and then expires unless Congress extends it.
What it does not do is touch the combined-income formula or the three bands above. Those rules are unchanged. The deduction works downstream, by shrinking the taxable income that results, which is enough to wipe out the tax for many retirees with modest income. The Treasury estimates that with this deduction layered on top of the existing standard and senior deductions, about 88% of beneficiaries will owe no federal tax on their benefits during the four-year window. The other side of that figure is the part worth planning around: it is temporary, it phases out for higher earners, and the underlying tax returns in full in 2029.
You cannot change the thresholds or the formula. You can change what flows into your adjusted gross income, which is the largest component of the formula.
Qualified withdrawals from a Roth IRA or Roth 401(k) do not appear in adjusted gross income, so they never enter combined income. A dollar pulled from a traditional IRA raises your combined income and can drag more of your benefit into a taxable band. The same dollar pulled from a Roth account does neither. Two retirees with identical spending can owe very different tax on the same benefit purely because of which accounts they draw from first. That is the core argument for holding both Roth and traditional accounts rather than betting everything on one.
This is also why the order you tap accounts matters as much as how much you withdraw. RetirFi's calculator draws your accounts down in a tax-aware sequence and models the tax on your benefits year by year, so you can see how shifting a withdrawal from a traditional account to a Roth changes the lifetime tax bill. When to claim is a separate question, covered in our guide on the break-even age for claiming at 62, 67, or 70.
Everything above is federal. States set their own rules, and the federal treatment tells you nothing about your state's. The large majority of states do not tax Social Security at all. A small and shrinking number still do, each with its own carve-outs tied to age or income, and several have phased their tax out in recent years. If you are choosing where to retire or estimating your real after-tax income, check your specific state's rule rather than assuming the federal answer carries over.
Whether your Social Security is taxed is not random and it is not fixed. It tracks one number, your combined income, and you have real control over the largest input to that number through which accounts you draw from and in what order. The frozen thresholds mean the question matters more for each new cohort of retirees, and the 2025 senior deduction offers temporary relief that fades after 2028. The way to see what all of this means for your own checks is to put your actual numbers in. Enter your benefit, your account balances, and your spending in the RetirFi calculator and watch how the drawdown order moves your tax on Social Security across a full retirement.
Enter your numbers and run a Monte Carlo simulation to see how this plays out for your specific timeline and assets.
Run the Calculator →