Clear Money Guide
What this guide covers
A quick view of the questions and evidence developed below.
Updated July 28, 2026. Quick answer: A conversion raises provisional income, and provisional income determines how much of your Social Security benefit is taxable. Within certain ranges each additional conversion dollar can make an additional portion of your benefit taxable too — producing an effective rate materially above your stated bracket.
The stacking effect
Social Security is taxed based on provisional income. As that rises through certain ranges, a larger share of the benefit becomes taxable. So a conversion dollar can do two things at once: be taxed itself, and drag part of a benefit into taxation alongside it.
The result is an effective marginal rate on that range that is meaningfully higher than the bracket table shows — sometimes strikingly so.
This is the strongest argument for converting before claiming Social Security. In the years between retiring and claiming, there is no benefit to drag into taxation, so the conversion is taxed at its face rate and nothing else moves.
Once you are already claiming
The effect does not make conversions wrong, but it changes the sizing: the cost of the next dollar converted is not your bracket, it is your bracket plus whatever benefit it pulls in. Model the whole return rather than the bracket.
Our provisional income calculator computes the input this all turns on.
Price the conversion before you make it
A conversion cannot be undone once it is done, so it is worth having someone model the bracket it fills, the knock-on effects on your other income and how long the money has to compound before you settle on an amount.
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Sources
IRC §408A (Roth IRAs); IRC §408A(d)(3) (conversions); IRC §1411 (net investment income tax); IRC §86 (taxation of Social Security benefits); IRC §6654 (estimated tax); Tax Cuts and Jobs Act (2017) §13611 (repeal of conversion recharacterisation). Cross-checked July 2026 against professional analyses. Indexed thresholds are described rather than asserted, because they change annually.
This states what the cited authority says. It is not tax advice, and a conversion interacts with the rest of your return in ways one page cannot see.
Related
When each additional dollar can pull more of a benefit into tax, the useful question is where to stop rather than how far to go. The Roth conversion guardrail estimator takes a ceiling you want to stay under, together with your taxable income before the conversion and your marginal rate, and returns the room left beneath that ceiling and the estimated tax on using it. Its optional cap field is labelled for Medicare’s IRMAA, but arithmetically it is simply a ceiling you set.