Most retirees discover the rule the hard way: a modest RMD, a certificate of deposit rolling at a higher rate, or a one-time IRA withdrawal quietly pushes them across a threshold that turns a chunk of their Social Security benefit into taxable income. The mechanism behind that surprise is called provisional income — and for 2026, the thresholds that trigger it are exactly where Congress set them more than four decades ago.
The Thresholds That Never Moved
Under Internal Revenue Code §86, Social Security benefits are taxed based on a provisional income figure. For single filers, provisional income under $25,000 keeps benefits federally tax-free. Between $25,000 and $34,000, up to 50% of benefits become taxable. Above $34,000, up to 85% can be taxed. For married couples filing jointly, the tiers are $32,000 and $44,000.
The 50% tier was written into law in 1983. The 85% tier was added in 1993. Neither figure is indexed for inflation, and neither has been adjusted since. Federal tax brackets, IRA contribution limits, the standard deduction, and Social Security's own wage base all rise every year. These four numbers do not.
The practical consequence: a benefit that was firmly tax-free for a typical retiree in the 1980s now routinely triggers the 85% tier for middle-income households in 2026. When the Congressional Research Service and the Social Security Trustees have modeled the drift, they have consistently projected a rising share of beneficiaries owing tax on some portion of benefits over time.
How the Number Is Calculated
Provisional income is not the same as adjusted gross income. The formula is:
AGI + tax-exempt interest + 50% of total Social Security benefits.
Two elements catch retirees off guard. First, tax-exempt municipal bond interest is added back in — muni income does not increase your regular tax bill, but it can absolutely increase the taxable portion of your Social Security. Second, half of the Social Security benefit itself is part of the calculation, which is why a large benefit alone can push a household toward the taxable tiers before any other income is considered.
What Changed for 2026: The OBBBA Senior Deduction
The One Big Beautiful Bill Act, signed in July 2025, created a new $6,000 per-person deduction for taxpayers age 65 and older, available for tax years 2025 through 2028. Because the deduction reduces AGI, and AGI is the starting point of the provisional income calculation, it also reduces provisional income. For lower- and middle-income retirees, the deduction can move the household below one of the §86 thresholds and eliminate or reduce Social Security taxation entirely.
The deduction phases out at higher income levels, so its usefulness fades exactly where the taxation problem is largest. But for households sitting near a threshold, it is a meaningful new lever for 2026.
Practical Strategies
Because the thresholds are fixed, planning is about controlling the inputs. Several approaches are worth reviewing before the end of the tax year.
- Prefer Roth withdrawals when near a threshold. Qualified Roth IRA and Roth 401(k) distributions are not included in AGI, and therefore not in provisional income. A retiree with both traditional and Roth balances can meaningfully change their Social Security tax outcome simply by choosing which bucket to draw from.
- Use Qualified Charitable Distributions to satisfy RMDs. A QCD (available starting at age 70½) transfers IRA funds directly to a qualified charity. The distribution counts toward the required minimum distribution but is excluded from AGI, avoiding the provisional income bump that a normal RMD would create.
- Rethink the role of municipal bonds. Munis remain useful for state-tax reasons and for pure federal-income savings, but retirees who assume they are entirely "invisible" for tax planning should model the actual provisional income effect before overweighting them.
- Consider Roth conversions in low-income years. The years between retirement and the start of Social Security or RMDs are often the lowest-income window a retiree will ever see. Converting traditional IRA balances to Roth during that window shifts future withdrawals out of the provisional income calculation permanently.
- Watch the timing of one-time events. A large capital gain, a CD maturity, or a lump-sum pension election can push a normally comfortable household across a threshold in a single year. Spreading realizations across tax years, when possible, keeps provisional income smoother.
The Bigger Picture
The 1983 and 1993 thresholds were originally designed to affect only higher-income beneficiaries. Because they were never indexed, the population they reach expands almost automatically each year — through no policy change at all. That is the quiet part of retirement tax planning that most benefit statements do not mention.
For retirees building a distribution strategy, provisional income is not a footnote. It is the number that determines how much of a lifetime of Social Security contributions actually stays in the household.
Sources: Internal Revenue Service, Social Security Administration, Stonewood Financial, Kiplinger, Fidelity