The Tax Thresholds Nobody Indexed, and What They Cost Retirees
The income levels that determine how much Social Security benefit is taxable have not moved since the 1980s and 1990s, pulling a growing share of ordinary retirees into a tax designed for the affluent.
Almost every meaningful number in the federal tax code moves with inflation. Brackets, the standard deduction, retirement contribution limits, the estate tax exemption — all adjust annually.
Three numbers do not. The thresholds that determine how much of a Social Security benefit is subject to federal income tax were set in 1983 and expanded in 1993, and they have never been indexed.
How the math works
The calculation uses "combined income" — adjusted gross income plus tax-exempt interest plus half of Social Security benefits. Above the first threshold, up to half the benefit becomes taxable. Above the second, up to 85% does.
When the higher tier was enacted, it was designed to reach a small minority of beneficiaries with substantial income from other sources. Because the thresholds are fixed in nominal dollars and benefits rise with a cost-of-living adjustment every year, the same real income crosses the line year after year.
This year's adjustment was 2.8%, lifting benefits for roughly 71 million people by about $56 a month on average. That increase itself pushes some recipients across a threshold.
The interaction that surprises people
Because the benefit's taxability depends on other income, an additional dollar of withdrawal from a retirement account can make more of the benefit taxable — producing an effective marginal rate well above the stated bracket for retirees in a particular income band.
Planners spend a great deal of time on this. The standard approaches involve managing the timing of withdrawals, converting to Roth accounts in low-income years before required distributions begin, and where possible, coordinating the age at which benefits are claimed with the drawdown sequence.
Why it never gets fixed
Indexing the thresholds would reduce revenue to the Social Security and Medicare trust funds, which receive the proceeds of this tax. Given the funds' long-run shortfalls, no proposal to reduce their income advances easily.
The result is a policy that raises revenue through inaction rather than legislation — the modern equivalent of the bracket creep that indexing was introduced to eliminate.
