The Social Security Tax Torpedo: When Your Marginal Rate Jumps

Take $1,000 more out of a traditional IRA. In the 12% bracket you would expect $120 of federal tax. For a large group of retirees the bill is $222. Some pay $407. The gap comes from Social Security, and it has a nickname: the tax torpedo.

How the torpedo works

The IRS taxes Social Security benefits using provisional income: your adjusted gross income, plus tax-exempt interest, plus half of your benefits. The guide to how Social Security is taxed sets out the thresholds. Below the first, benefits are tax-free. Between the first and second, up to 50% of benefits can become taxable. Above the second, up to 85%.

The trap sits in the stretch where benefits are still becoming taxable. Inside it, an extra dollar of other income is taxed as income in its own right and at the same time moves another slice of your Social Security check from the untaxed column into the taxed one, so the return shows more income than the dollar you actually withdrew. In the upper zone the slice is up to 85 cents. One IRA dollar becomes $1.85 of taxable income.

The arithmetic

A retiree who thinks of themselves as a 12% taxpayer is paying 22.2% on the margin. In the 22% bracket it’s over 40%. That’s a rate people associate with very high earners, charged here on income that may be modest by any other measure.

In the lower zone the pull is 50 cents per dollar. The same $1,000 then adds $1,500 of taxable income. In the 12% bracket, that’s $180. An 18% rate.

The torpedo does end. Once 85% of your benefit is taxable, no more of it can be pulled in, and from there each extra dollar is taxed at the plain bracket rate again, which gives the marginal rate an odd shape: it climbs through the middle of the retirement income range, peaks while the benefit is being drawn in, and falls back once the cap is reached.

Who meets it

Middle-income retirees are in the path. Low incomes stay below the first threshold. High incomes are already at the 85% cap. The people caught are those with a Social Security check plus a traditional IRA or 401(k) that they draw from every year, often in amounts sized for spending with no thought about where they land against the thresholds.

It gets worse later. Required minimum distributions can force withdrawals into the zone whether you need the money or not.

Ways around it

Roth money is the cleanest fix. Qualified Roth IRA withdrawals stay out of adjusted gross income. They add nothing to provisional income, so a retiree who takes a year’s spending money from a Roth while sitting near the thresholds can leave the benefit untaxed or lightly taxed and keep the traditional IRA for years when the arithmetic is kinder. The course on growing money in Roth and HSA accounts covers the Roth withdrawal rules.

Convert before you claim. Roth conversions are taxable in the year you make them. Done in the years between retiring and starting Social Security, they carry no benefit interaction at all, because there are no benefits yet to pull in.

Time the IRA withdrawals. Draw more from the IRA before claiming Social Security, delaying the claim and shrinking the IRA. Or, once collecting, bunch withdrawals: a big year that pushes past the zone to the 85% cap, alternating with lean years spent from savings or Roth money, can cost less than steady withdrawals that land in the torpedo every year.

Situations differ, and the right move depends on the whole return. The guide to choosing a Roth or traditional IRA covers the bracket side of the same decision.

Required minimum distributions are the part of this you don’t control, and the next lesson on required minimum distributions shows how large they get.