Guide · Social Security
Will converting push more of your Social Security into taxable income?
The Social Security "tax torpedo" is invisible in your nominal tax bracket — a household that looks like it's in the 22% bracket can face a real marginal rate on conversion dollars closer to 40%. Here's what drives it and how to sequence around it.
What "provisional income" means
Up to 85% of a household's Social Security benefit can become taxable, and how much depends on provisional income — AGI, plus tax-exempt interest, plus half of the Social Security benefit itself. As provisional income climbs through two statutory thresholds, the taxable share of benefits rises from 0% toward that 85% ceiling. For 2026 those thresholds sit at $32,000 and $44,000 for married-filing-jointly households ($25,000 and $34,000 single), and unlike most tax parameters they aren't indexed for inflation — so they capture more of every benefit dollar each year.
Why it's called a torpedo
Inside the phase-in range, each additional dollar of ordinary income — including Roth conversion income — can drag an extra $0.50 to $0.85 of Social Security benefit into taxable income on top of the conversion dollar itself. That stacking effect produces a real marginal rate well above the stated bracket, commonly cited around 1.5x to 1.85x the nominal rate at the worst part of the range. A household nominally in the 22% bracket can face something closer to 35-40% on the conversion dollars that fall in that zone.
The sequencing lever
The torpedo only applies in years Social Security benefits are actually being received. That timing is the single biggest lever a household has: conversions done before claiming Social Security avoid the torpedo entirely for those years. It's a common reason to front-load conversions into the gap between retirement and claiming, rather than spreading them evenly across the whole horizon.
A worked example
A married couple receiving $46,000 in combined Social Security has $40,000 of other income, putting provisional income at $40,000 (other income) + $23,000 (half of SS) = $63,000 — deep in the phase-in range. A $10,000 Roth conversion doesn't just add $10,000 of ordinary income; it can drag roughly $7,000-$8,500 more of their Social Security into taxable income alongside it, so the true taxable-income increase is closer to $17,000-$18,500 for a $10,000 conversion. Converting the same $10,000 the year before claiming avoids that drag completely.
How Harbor handles it
Harbor computes taxable Social Security exactly as the IRS worksheet does, on both the no-conversion and with-conversion paths, and flags it directly whenever a modeled conversion drags more benefit into taxation. The torpedo's inflection point becomes one of the walls the schedule optimizer respects, so a plan that looks efficient on the nominal bracket doesn't quietly cost more once the real marginal rate is counted.
See your real marginal rate
Harbor shows the torpedo-adjusted cost of every conversion dollar, not just the bracket rate.
Start planning — it's free →Common questions
Will converting push more of my Social Security into taxable income?
Yes — extra income raises provisional income and can drag more of your Social Security benefit into taxation (the "tax torpedo"). Harbor measures how much of your benefit becomes taxable at each conversion size.
Can I avoid the Social Security tax torpedo entirely?
The torpedo only applies in years you're actually receiving Social Security, so converting before you claim avoids it for those years. Once you're claiming, Harbor still shows you the real marginal cost so it isn't a surprise.