When Social Security starts, it doesn’t just add income — it makes every other dollar you earn more expensive.
Most retirees think of Social Security as one income stream among several, taxed on its own terms. But the tax code doesn’t see it that way. A formula called provisional income determines how much of your benefit gets taxed — and once you’re drawing Social Security, that formula quietly reshapes the cost of every withdrawal, conversion, or paycheck that comes after it.
Here’s exactly how that works.
How Social Security Taxation Works
Whether any of your Social Security benefit is taxed comes down to a specific formula the IRS calls “combined income,” though most planners just call it provisional income: adjusted gross income plus tax-exempt interest plus 50% of your Social Security benefits. It’s not a number that shows up on a bank statement or a line item you’d recognize — it exists only to answer one question: how much of your benefit counts as taxable income.
For 2026, the thresholds that answer that question are:
- Single filers and married filing separately: below $25,000 in provisional income, 0% of benefits are taxable; between $25,000 and $34,000, up to 50% becomes taxable; above $34,000, up to 85% can be taxed.
- Married filing jointly: below $32,000, 0% taxable; between $32,000 and $44,000, up to 50% taxable; above $44,000, up to 85% taxable.
The detail that matters most for planning: these thresholds haven’t moved with inflation since 1984. They were fixed in the original statute and have simply stayed in place while wages, COLAs, and account balances have grown around them. That means a retiree who felt comfortably below the threshold a decade ago can drift into taxable territory over time — not because they did anything different, but because the line never moved with inflation.
Why the Next Dollar Costs More
Once you’re inside the phase-in range — the $25,000–$34,000 band for single filers, $32,000–$44,000 for joint filers — an extra dollar of other income doesn’t just get taxed once. It does double duty: it’s taxed directly, and it can simultaneously pull a portion of your Social Security benefit into taxable income alongside it. In the phase-in zone, every additional dollar of income can make an additional $0.50 to $0.85 of previously untaxed Social Security benefit taxable as well.
The effect on your real, effective tax rate can be sharp. A retiree whose stated bracket reads 12% can find that every extra dollar of IRA income drags an additional $0.85 of Social Security into taxable income, turning one dollar into $1.85 of new taxable income — a real marginal rate closer to 22%, not 12%. Retirees who assume the 22% bracket is their ceiling can be surprised to find an effective marginal rate of 40.7% or more on the next dollar they withdraw, once the Social Security phase-in is layered on top of it. Planners sometimes call this the “tax torpedo” — an effective marginal rate that can reach 22.2%, 27.75%, or even 40.7%, depending on where in the phase-in range a retiree sits.
To be clear: this is a mechanical feature of the tax code, not a fixed outcome — the exact impact depends entirely on your specific income mix, filing status, and where you fall relative to the thresholds. The example above illustrates how the stacking works, not what any individual retiree should expect to pay.
That’s the real cost of claiming Social Security: it isn’t that the benefit itself is expensive to receive. It’s that receiving it changes the price tag on everything else.
Where This Shows Up in Real Decisions
Once you see the mechanics, the planning implications follow directly.
- Roth conversion timing. Money converted and withdrawn from a Roth account later doesn’t count as income against the provisional income formula, so it never re-triggers the phase-in.
- Withdrawal order. Pulling from a traditional IRA versus a taxable brokerage account versus a Roth account in a given year can shift how much Social Security becomes taxable that year, even if total spending is identical.
- Municipal bonds. Retirees often hold munis specifically because the interest is federally tax-exempt — but that exemption doesn’t extend to the provisional income calculation. Tax-exempt interest is added back in when the IRS determines how much of your Social Security benefit is taxable, so a large muni bond position can still push someone into the phase-in range even though the interest itself was never taxed directly.
- Claiming age. Delaying doesn’t avoid the tax torpedo entirely, but it changes when the stacking effect starts relative to other income sources like continued work, pension payments, or required IRA withdrawals.
None of these decisions works in isolation. Roth conversion timing, withdrawal sequencing, and claiming age are connected — a change to one shifts the math on the others, which is why they’re usually best worked through together rather than one at a time.
The 2026 Senior Deduction: A Temporary Offset
One recent change is worth noting, mostly because clients are already asking about it. The One Big Beautiful Bill Act, signed in July 2025, added a new $6,000 per-person deduction for taxpayers age 65 and older, available for tax years 2025 through 2028.
The deduction doesn’t touch the provisional income thresholds themselves — those stay exactly where they’ve been since the 1980s. What it does is lower adjusted gross income, which is one of the three inputs to the provisional income formula. For retirees sitting close to a threshold, that reduction can be enough to keep some or all of Social Security out of taxable income for the years the deduction is in effect.
It’s a useful, current piece of the picture — but it’s temporary by design, and it doesn’t change the underlying mechanics described above. It’s worth factoring into near-term planning, not treated as a permanent fix.
This article is educational and general in nature. It isn’t individualized tax, investment, or legal advice — your own situation should be reviewed with a qualified professional before you act.
Turning Awareness Into a Plan
These thresholds have stayed fixed for four decades, with nothing in current law suggesting a change is imminent. That leaves timing and sequencing — of Roth conversions, withdrawal order, and claiming age — as the levers retirees have any real control over.
If you’d like to explore how coordinated retirement income and tax planning might apply to your situation, you can request a Fit Meeting with Paul Axberg at Axberg Wealth. This introductory conversation is designed to review your priorities, look at how decisions like distribution timing, withdrawal order, and Social Security timing fit together, and determine whether working together is an appropriate mutual fit — without assumptions or commitments.
Disclosures
The opinions expressed herein are not meant to provide specific investment advice or serve as a prediction for future stock market performance. We recommend everyone consult with a financial professional for advice related to their own, individual financial situation or plan. Paul Axberg is an investment advisor representative of, and securities and advisory services are offered through USA Financial Securities, Member FINRA/SIPC. A registered investment advisor located at 6020 E. Fulton St., Ada, MI 49301. Axberg Wealth Management is not affiliated with USA Financial Securities.