The most common answer to "how much should I convert to a Roth each year" is also the most practical: fill your current tax bracket and stop. Add up this year's taxable income, subtract it from the top of the bracket you are willing to pay, and the difference is your conversion room. It is one subtraction. The hard part is everything the subtraction does not see.
Here is the method with 2026 figures. Project this year's taxable income before any conversion: gross income minus deductions, including the 2026 standard deduction of $32,200 for married couples filing jointly. Pick a target ceiling. The top of the 12% bracket is $100,800 of taxable income for joint filers; the top of the 22% bracket is $211,400. Subtract your projected income from the ceiling. That gap is your bracket headroom.
A worked example makes it concrete. A married couple with $120,000 in taxable income sits in the 22% bracket, which runs to $211,400. Their headroom is $91,400. Converting exactly that amount moves $91,400 into the Roth at 22%, about $20,108 in federal tax, without letting a single dollar spill into the 24% bracket. Convert $100,000 instead and the last $8,600 gets taxed at 24%. The bracket is a container. The headroom tells you how much it holds.
Bracket headroom is not the only line
The bracket ceiling is the line you chose. There are lines you did not choose, and for retirees they are often closer. Medicare's IRMAA surcharge is a cliff, not a slope: in 2026, a married couple with modified adjusted gross income above $218,000 pays higher Part B and Part D premiums, and the lookback runs two years, so a 2026 conversion sets your 2028 premiums. The 3.8% net investment income tax starts at $250,000 of MAGI. If you have claimed Social Security, conversion income can push more of each check into taxable territory at the $32,000 and $44,000 combined-income thresholds, which have never been indexed for inflation.
Two more, because they are new. Through 2028, each taxpayer 65 or older gets an extra $6,000 senior deduction, but it shrinks above $150,000 of income for couples ($75,000 single), so a conversion dollar in that range costs a little more than the bracket rate suggests. And if you buy health insurance on the marketplace before 65, the premium subsidy has a hard cutoff at 400% of the poverty line again, since the enhanced subsidies expired at the end of 2025. Cross it and the subsidy can drop to zero, often a far larger cost than the tax on the conversion itself.
So the working rule: convert up to the lowest binding line, not the highest bracket you can stomach. Compute the headroom, check each threshold, and convert to whichever bites first. Run the math in October or later, when the year's income is mostly known. And remember the conversion cannot be undone. Recharacterization ended with the 2017 tax law, so an overshoot stands for the year.
The one time I would cross a line on purpose: when you know future rates will be higher anyway. A big traditional IRA facing required minimum distributions at 73 can push you into a higher bracket every year for the rest of your life. Paying 24% now to avoid 32% later is not an error. It is the same math, run forward.
You can model conversion amounts and the five-year clocks with the free Roth conversion ladder calculator.
Plan your Roth conversion ladder
Frequently asked questions
Is there a limit on how much I can convert to a Roth IRA?
No. The IRS sets no cap on conversion amounts. The practical limit is bracket headroom: the gap between your taxable income and the top of the bracket you are willing to fill.
Does a Roth conversion count as income?
Yes. The converted amount is treated as ordinary income in the year of the conversion, which is why a large conversion can push part of your income into a higher bracket.
Can I undo a Roth conversion?
No. Recharacterizing a Roth conversion was eliminated by the 2017 Tax Cuts and Jobs Act. Once you convert, the decision is final for that tax year.
What happens if I convert too much?
Only the dollars above the bracket threshold are taxed at the higher rate, not the whole conversion and not the rest of your income. Because the conversion cannot be reversed, the extra tax stands for that year.
When in the year should I convert?
October through December is the usual window, because most of the year's income is known by then and you can size the conversion against the actual headroom remaining.
Sources: IRS Revenue Procedure 2025-32 (2026 tax brackets); IRS Publication 915; CMS 2026 Medicare premium fact sheet. Bracket worksheet method via q3adv.com; thresholds via levyio.com and millswealthadvisors.com. Verified October 2026.