Why a Roth Conversion or “Tax‑Free” Interest Can Raise Social Security Taxes
Your Social Security deposit can look the same throughout the year. Then you complete a Roth conversion, or tax-exempt municipal-bond interest appears on a year-end statement.
The monthly benefit did not change. The tax return may. Both items can raise combined income, which may cause more of your Social Security benefit to be included in taxable income.
How does other income reach your Social Security benefits?
A Roth conversion generally moves money from a traditional IRA into a Roth IRA. To the extent the converted money has not already been taxed, it is generally included in gross income for that year.[1] The Roth account may support qualified tax-free withdrawals later, but that future treatment does not make the conversion tax-free today.[2]
Municipal-bond interest enters from a different direction. The interest may be exempt from federal income tax, yet the Social Security calculation still adds it as tax-exempt interest.[3]
What enters the combined-income calculation?
The calculation commonly called combined income adds adjusted gross income before taxable Social Security, tax-exempt interest, and one-half of annual Social Security benefits. For a joint return, both spouses' income and benefits are included. That remains true when only one spouse receives Social Security.[4]
How can two different items produce the same tax effect?
The routes differ, while the Social Security calculation responds to both.
Income item | Monthly benefit | Combined income | Possible return effect |
|---|---|---|---|
Taxable Roth conversion | Unchanged | Generally rises through adjusted gross income | More benefits may become taxable |
Tax-exempt municipal-bond interest | Unchanged | Rises through the tax-exempt-interest add-back | More benefits may become taxable |
The federal thresholds work in two tiers for the filing statuses most retirees use. For single filers, combined income from $25,000 through $34,000 can make up to 50 percent of benefits taxable. Above $34,000, up to 85 percent can be taxable. For married couples filing jointly, the corresponding ranges are $32,000 through $44,000 and above $44,000.[5]
The 50 percent and 85 percent figures describe how much of the benefit may enter taxable income. Regular federal tax rules then determine the tax due. A temporary deduction for some taxpayers age 65 or older may reduce taxable income through 2028. It leaves the combined-income formula and thresholds unchanged.[6]
Dovetail Principle: Information Should Show What Changes for You
“Tax-free” describes the treatment of one item. It does not describe everything that item can change. The useful information is the chain of effects: whether combined income rises, whether more Social Security becomes taxable, and whether the household's projected tax changes.
What can a Roth conversion change in a simple example?
Suppose a married couple receives $24,000 of Social Security and has $30,000 of other income. With no tax-exempt interest or special adjustments, combined income is $42,000. The federal worksheet would include $5,000 of Social Security in taxable income.
A fully taxable $10,000 Roth conversion raises combined income to $52,000. The taxable portion of Social Security rises to $12,800. The conversion adds $10,000 of taxable income and causes another $7,800 of Social Security to enter taxable income in this simplified illustration.[6]
The final tax bill still depends on deductions and the rest of the return. The example gives the couple a better basis for deciding how much to convert this year and what could wait.
What belongs in the year-end projection?
Before year-end, place the taxable portion of a planned conversion alongside IRA withdrawals, pension income, wages, realized gains, investment income, and tax-exempt interest. Then compare conversion amounts or timing choices using the same assumptions.
The projection can show the effect on taxable Social Security and the estimated federal tax. It can also indicate whether payments during the year deserve attention. Social Security permits federal withholding of 7, 10, 12, or 22 percent of the monthly benefit.[7] Quarterly estimated tax payments are another option.[8]
A Roth conversion may still support a worthwhile long-term purpose. Municipal bonds may still suit the investment and income plan. Reviewing the tax effect during the year preserves room to decide how each choice should be used.
For a broader look at the decisions surrounding retirement income, visit Dovetail's Retirement Tax Planning page.
Related Reading: Can a Roth Conversion Affect Health Coverage Costs? That article follows the same conversion income into a different retirement cost.
