A bigger cost-of-living adjustment raises your Social Security benefit, but the income thresholds that decide whether those benefits are taxed never move. Because the thresholds are frozen in nominal dollars, every raise pushes a little more of your benefit across them — so a COLA can hand you more gross income and a larger tax bill at the same time. The Social Security Administration's own research is blunt about the mechanism: the taxable-income thresholds "are not indexed to changes in prices or wages." That single design choice is why a benefit increase meant to preserve purchasing power can quietly shrink what you actually keep, and why the share of retirees paying tax on benefits has climbed for four decades.
Table of Contents
- The thresholds that decide whether your benefits are taxed
- How one COLA moves you across the line
- Who this is actually hitting
- A temporary offset that expires after 2028
- Medicare premiums take a second bite
- What to check before the 2027 raise lands
- Frequently Asked Questions
The thresholds that decide whether your benefits are taxed
Social Security uses a figure called combined income: your adjusted gross income, plus any tax-exempt interest, plus half of your annual benefits. According to the SSA's retirement tax planner, benefits start becoming taxable once combined income passes $25,000 for a single filer or $32,000 for a couple filing jointly. In that first band, up to 50% of your benefits can be taxed.
Above $34,000 single or $44,000 joint, up to 85% of benefits becomes taxable income. Note what is taxed: not 85% of your benefit in tax, but 85% of the benefit counted as ordinary income at your marginal rate. Those four dollar figures have not changed since they were written — $25,000 and $32,000 date to 1983, the $34,000 and $44,000 tier to 1993. A benefit indexed to inflation measured against a threshold that is not indexed produces a predictable, one-way result.
How one COLA moves you across the line
Start with the raise itself. The SSA's 2026 COLA fact sheet put this year's adjustment at 2.8%, based on CPI-W growth from the third quarter of 2024 to the third quarter of 2025, applied to benefits for nearly 71 million people from January 2026. The maximum benefit at full retirement age rose from $2,015 to $2,071 a month. The 2027 figure is not official yet. SSA announces it after September CPI-W data, expected October 14, 2026, and outside estimates cluster between 3.2% and 3.6% — The Senior Citizens League predicts 3.5%.
Now apply that to a single filer sitting just under a line. Half of a benefit counts toward combined income, so a 3.5% raise on a $24,000 annual benefit adds roughly $840 in benefits and about $420 to combined income. If that filer was at $24,800 in combined income, the raise alone carries them over $25,000 and makes part of the benefit taxable for the first time. Two things make this worse than a single year suggests. The raise is permanent, so you stay over the line in following years. And the pension, annuity, or required minimum distribution on the other side of your income usually grows too.
Who this is actually hitting
This is no longer an edge case for high earners. The Congressional Budget Office estimates that 48% of Social Security beneficiaries will owe income tax on their benefits in 2026 — up from roughly 8.4% of beneficiary families in 1984, the first year the tax applied. The aggregate numbers show the same drift. A CBO budget spotlight published in August 2026 projects income taxes on benefits at $120 billion in 2026, equal to 7.1% of all benefits paid, rising to 9.0% of benefits by 2056.
CBO names the fixed nominal thresholds as the main driver. The people most exposed are retirees with modest outside income: a small pension, part-time work, interest, or a required distribution that lands them within a few thousand dollars of $25,000 or $32,000 in combined income. Retirees whose only income is Social Security generally stay under the thresholds. Retirees well above them are already taxed on 85% and have nothing left to cross.
A temporary offset that expires after 2028
One current provision cushions much of this, and it has an end date. Under the One Big Beautiful Bill Act, the IRS describes an enhanced deduction for seniors worth up to $6,000 per filer aged 65 or older — $12,000 for a qualifying couple — available whether you itemize or not. The deduction phases out above $75,000 modified AGI for single filers and $150,000 for joint filers.
For 2025 through 2028, it can wipe out the tax a COLA would otherwise trigger for many middle-income retirees. Two limits matter for planning. The deduction expires after 2028 unless Congress extends it. And it does not touch the $25,000 and $32,000 thresholds themselves, so the underlying drift continues underneath it — when the deduction lapses, filers will face the accumulated effect of several years of COLAs against unchanged thresholds.
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Medicare premiums take a second bite
Taxes are not the only thing that eats a raise. Medicare's income-related monthly adjustment amount, or IRMAA, is a surcharge on Part B and Part D premiums for higher-income beneficiaries, and a COLA-inflated income year can push you over a bracket. The CMS 2026 Medicare Parts A and B fact sheet sets the first IRMAA threshold at $109,000 modified AGI for individuals and $218,000 for couples, up from $106,000 and $212,000 in 2025, with Part B surcharges reaching $487.00 a month at the top tier. IRMAA brackets are indexed, unlike the tax thresholds — but the timing is the trap.
SSA uses a two-year lookback, so your 2026 premium is set from your 2024 tax return. By the time a premium increase appears, the income year that caused it is two filing seasons behind you. The standard premium climbs too. The 2026 Medicare Trustees Report projects the standard Part B premium at $209.50 in 2027, up $6.60 from $202.90, and CMS has finalized a $700 Part D deductible for 2027, an $85 increase. Official 2027 Part B rates arrive in November 2026.
What to check before the 2027 raise lands
These are the checks worth running once the COLA is announced, while you still have time to act in the current tax year. If you expect to cross a threshold, the lever you control is the non-Social Security side of combined income: the timing of withdrawals, conversions, and asset sales. Tax-exempt municipal bond interest does not help here, because it counts toward combined income even though it is not taxable on its own.
- Calculate your combined income: AGI, plus tax-exempt interest, plus half your annual benefits. Compare it to $25,000 single or $32,000 joint, and to $34,000 and $44,000.
- Measure your distance to the nearest threshold. If you are within a few thousand dollars, the raise will likely move you across it.
- Check whether the enhanced senior deduction covers the difference for 2026, 2027, and 2028 — and model what happens in 2029 if it does not return.
- Look at the income year that will set your Medicare premiums two years out, not just this year's. A one-time Roth conversion or asset sale is what usually trips IRMAA.
- If a life-changing event cut your income after the lookback year — retirement, a spouse's death, loss of a pension — SSA Form SSA-44 exists to have IRMAA recalculated on current income instead.
Frequently Asked Questions
Does a COLA mean 85% of my benefit gets taxed in tax?
No. Above $34,000 combined income single or $44,000 joint, up to 85% of your benefit is counted as taxable income and then taxed at your ordinary marginal rate. The tax owed is a fraction of that amount, not 85% of the benefit.
Would declining the COLA keep me under the threshold?
Social Security does not offer that option, and it would not help. The raise is applied automatically to all benefits. The practical lever is the timing of your other income — withdrawals, conversions, and sales — not the benefit itself.
Will the thresholds ever be indexed to inflation?
They are unchanged since 1983 and 1993, and CBO's projections through 2056 assume they stay fixed in nominal dollars. Any change would require new legislation.
Can I avoid this by holding municipal bonds?
No. Tax-exempt interest is added back into the combined-income formula alongside AGI and half of your benefits, so municipal interest counts toward the thresholds even though it is not itself taxed.
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