Updated July 28, 2026. Quick answer: An unusually low-income year is the cheapest time to convert, because you are filling brackets that would otherwise go unused. A gap year, a redundancy, a start-up year or the window before Social Security all qualify.
Filling brackets that would otherwise be wasted
Brackets do not carry forward. Income that could have been taxed in a low bracket this year and was not is simply taxed at a higher rate later. A low-income year is an expiring opportunity, not a neutral one.
| Situation | Why it is a window |
|---|---|
| Between jobs or on sabbatical | Little or no earned income |
| Business start-up year | Losses can offset conversion income directly |
| Retired, pre-Social-Security | Widest brackets most people ever have |
| Retired, pre-RMD | Before forced income arrives on top |
The obvious caution: converting in a year you are short of money means finding the tax from somewhere. If you cannot pay it from outside funds, convert less rather than withholding from the conversion — especially under 59½, where the withheld portion can attract a penalty.
The unemployment trap
If you are on marketplace health insurance during the low-income year, the conversion can cost far more in lost premium subsidy than in tax. That is frequently the binding constraint precisely when income is lowest.
Sources
IRC §408A (Roth IRAs); IRC §408A(d)(3); IRC §402(c)(11) (inherited plan amounts); IRC §170 (charitable deduction); IRC §172 (net operating losses); SECURE Act (2019) and final RMD regulations published 19 July 2024. Cross-checked July 2026 against professional analyses. Indexed thresholds, aid formulas and state Medicaid rules are described rather than asserted — they change annually and by state.
This states what the cited authority says. It is not tax advice.