Tax-Optimized Withdrawals, Part 4: The Social Security Tax Torpedo

By Tom, CPA · Updated October 25, 2026

TL;DR: Once Social Security starts, each extra dollar of IRA income can also make up to 85 cents of benefits taxable. In that zone a 12% bracket behaves like 22%, and a 22% bracket like roughly 40%. Shrinking tax-deferred balances before claiming is the main defense.

Educational only, not tax, legal, or investment advice. Examples are illustrations, not predictions. Rules and limits change; verify current figures and talk to a qualified professional about your situation.

Meet a tax bracket that behaves like a 40% bracket while wearing a 22% name tag. It does not appear in any rate table. It is created by the way Social Security benefits become taxable, and it ambushes retirees who thought they had their bracket figured out.

Planners call it the tax torpedo. It is not a separate tax. It is a side effect of a formula written in the 1980s and 1990s whose dollar thresholds have never been adjusted for inflation. Every year, more retirees sail into it.

CPA Warning Label: The torpedo zone is narrow and moves with every dollar of income. Never eyeball it; run the IRS worksheet or a calculator.

How provisional income works

Whether your Social Security is taxable depends on a number usually called provisional income (the IRS worksheets do not use that label, but the math is the same). It is:

Adjusted gross income, not counting Social Security; + tax-exempt interest (yes, muni bond interest counts); + one-half of your Social Security benefits

IRS Topic 423 states the rule plainly: benefits are not taxable unless your modified AGI plus one-half of your benefits is more than the base amount for your filing status. Publication 915 contains the worksheet.

Notice what is in the formula. IRA withdrawals, Roth conversions, capital gains, dividends, interest and pension income all count. Roth IRA qualified withdrawals do not. That single difference is why Roth money is so valuable once benefits start.

The 50% and 85% thresholds (never indexed)

These figures come from Publication 915 and are set in the law itself. Unlike tax brackets, they are not adjusted for inflation, so the same $25,000 line that once caught only higher-income retirees now catches many middle-income ones. Social Security benefits themselves rise with inflation (benefits will increase 3.6% for 2027, SSA announced on October 14, 2026), which pushes more benefit dollars over the frozen lines every year.

Important: "85% taxable" means at most 85% of your benefits are included in income. It does not mean an 85% tax rate. No one pays tax on more than 85% of their benefits under this formula.

The torpedo zone illustrated

Illustration. Assumptions: single filer age 63 (so no age-65 extra deductions), $30,000 a year of Social Security, no other income except traditional IRA withdrawals, 2026 federal brackets and $16,100 standard deduction, no state tax.

Read the last column. Between roughly $25,000 and $42,000 of IRA withdrawals, this retiree is nominally in the 12% bracket but pays 22.2 cents per extra dollar, because each IRA dollar drags 85 cents of benefits into taxable income: 1.85 × 12% = 22.2%. Then, for a short stretch where she has crossed into the 22% bracket but benefits are not yet fully 85% taxable, each extra dollar costs 1.85 × 22% = 40.7%. Once 85% of benefits are taxable, the torpedo is spent and the marginal rate drops back to the ordinary 22%.

For a married couple with $40,000 of benefits, the same pattern shows a 22.2% marginal rate across a wide range of IRA withdrawals, dropping to 12% once benefits hit the 85% cap. The zone's location shifts with every household, which is why the Social Security taxable calculator exists.

Pre-claiming strategies

The torpedo hits households with substantial tax-deferred income on top of benefits. The defenses mostly happen before benefits begin:

• Roth conversions in the gap years. Every dollar converted before claiming is a dollar that will not later pull benefits into taxable income. Qualified Roth withdrawals are invisible to the provisional income formula.
• Spend down the IRA first, then claim later. Some retirees live on IRA withdrawals in their 60s while delaying Social Security, which also raises the eventual benefit. When benefits start, the IRA is smaller and the torpedo is weaker.
• Watch the municipal bonds. Tax-exempt interest counts in provisional income, so muni interest can make benefits taxable even though the interest itself is not. See munis for early retirees.
• Bunch, don't sprinkle. Sometimes it is cheaper to take a big IRA distribution in one year (blowing through the torpedo to the 85% cap) and very little the next, instead of medium amounts that sit in the zone every year. Run both versions.
• Use taxable account basis. Spending from cost basis in a brokerage account adds nothing to provisional income.

Who can ignore it

• Low-income retirees whose provisional income stays below $25,000 single or $32,000 joint. None of their benefits are taxable.
• High-income retirees who will always have 85% of benefits taxable no matter what. For them the torpedo is already "spent"; extra income is taxed at ordinary rates.
• Mostly-Roth households who can live on Roth withdrawals and basis once benefits start.

Everyone in the middle, which describes many FIRE households with a large 401(k), should model it. Lavish Larry learned about it from his tax return. Frugal Fran learned about it ten years earlier from a spreadsheet, and converted accordingly.

Claiming age and the torpedo

When you claim Social Security changes how long you live inside the torpedo zone. Claiming early means more years where benefits overlap with large IRA withdrawals. Delaying to 70 means a larger benefit later, but also more years before 70 when you can draw down the IRA or convert it with no benefits in the formula at all.

Picture Frugal Fran at 62. She has a $700,000 IRA and modest spending. If she claims at 62, every IRA dollar she takes for the next decade is partly taxing her benefits. If she waits until 70 and lives on IRA withdrawals and conversions in the meantime, she can push much of that IRA through the 10% and 12% brackets while the provisional income formula has nothing to bite. When her larger benefit finally starts, her remaining IRA is small, her required distributions are small, and she may land below the thresholds entirely or stay in the zone only briefly.

That is not a recommendation to delay; claiming decisions involve longevity, health, spousal benefits and cash needs that have nothing to do with tax. But the tax side of the decision is real and often overlooked. Lavish Larry claimed at 62 "to get his money back" and then spent eleven years paying a 22.2% marginal rate in a 12% bracket, which is a peculiar way to get money back.

Reading your own return for torpedo clues

You do not need software to spot whether you are in the zone. On last year's Form 1040, compare the gross Social Security amount on line 6a with the taxable amount on line 6b. If line 6b is zero, you are below the base amount. If it is exactly 85% of line 6a, you are past the torpedo and extra income is taxed at your ordinary bracket. Anything in between means you are in the zone, and every extra dollar of IRA income or capital gains is pulling more benefits into tax. That one comparison tells you more about your marginal rate than the bracket table does.

How this fits the rest of the series

The torpedo is one reason the bracket-filling approach in Part 3 focuses on the years before benefits begin. It also interacts with required distributions (Part 5), because RMDs are ordinary income that cannot be turned off, and with Medicare's income-based premiums (Part 6). The common thread: a smaller tax-deferred balance by the time benefits start gives you more control over every one of these lines.