Roth conversions · Sizing
How much of your IRA should you convert to Roth each year?
By Jim Swiech, CPA · Updated
Quick answer
Up to the lowest ceiling that applies to you this year, and not a dollar past it. There are five ceilings: the top of the tax bracket you are willing to pay, the Medicare income line two years out, the Social Security taxation zone if you are collecting, past 65 the income where the $6,000 senior deduction starts to phase out, and before 65 the marketplace premium-credit line if you buy your own health insurance.
For a married couple drawing $40,000 from an IRA with nothing else on the return, the 12% bracket has room for $93,000 of conversion in 2026, the 22% bracket for $203,600, and just under $178,000 before the first Medicare line.
Start with what is already on the return
A conversion is taxed on top of everything else you report that year, so the sizing question is really a subtraction. Add up the income you will have anyway: IRA withdrawals, pensions, interest, dividends, the taxable part of Social Security, a part-time paycheck. Subtract the standard deduction ($32,200 for a couple in 2026, more once either of you is 65). What is left is taxable income before the conversion. The conversion fills the space between that number and whichever ceiling you choose.
Our example couple is 63, retired, drawing $40,000 and collecting nothing else. Taxable income before any conversion is $40,000 minus $32,200, or $7,800. The 12% bracket ends at $100,800 of taxable income, so a $93,000 conversion fills it exactly. The 22% bracket ends at $211,400, so $203,600 fills that one.
The five ceilings
| Ceiling | Where it sits | What crossing it costs |
|---|---|---|
| Top of the 12% bracket | $100,800 taxable income | Next dollars taxed at 22% instead of 12% |
| Top of the 22% bracket | $211,400 taxable income | Next dollars taxed at 24% |
| First Medicare IRMAA line | $218,000 modified AGI | About $1,949 of Part B premium for a couple two years later, plus a smaller Part D surcharge, for one dollar over |
| Senior deduction phase-out (65+) | $150,000 AGI | Each spouse's $6,000 deduction shrinks 6 cents per dollar over the line |
| Marketplace premium credit (under 65) | Set each year by the federal poverty level and household size | The credit shrinks as income rises and can be lost entirely; check the line for your coverage year before converting |
The bracket ceilings are choices. Paying 22% now to avoid 24% later is a small win; paying 12% now to avoid 22% or more later is a large one. The Medicare line is not a choice, it is a cliff, and it is the one most people hit by accident because it is measured on modified adjusted gross income, not taxable income, and it takes effect two years after the conversion. The 2028 line will be indexed somewhat above $218,000, so treat $218,000 as the floor. If you are collecting Social Security, the taxation zone sits underneath all of these and raises the real rate on the first dollars converted.
What the ladder looks like for the example couple
| Conversion | Federal tax | Rate | New York | Crosses first Medicare line? |
|---|---|---|---|---|
| $25,000 | $2,660 | 10.6% | $358 | No |
| $50,000 | $5,660 | 11.3% | $1,535 | No |
| $100,000 | $12,360 | 12.4% | $4,285 | No |
| $150,000 | $23,360 | 15.6% | $7,035 | No |
| $200,000 | $34,360 | 17.2% | $9,897 | Yes, $240,000 modified AGI |
Notice the last row. At $200,000 the federal rate is still reasonable, but modified adjusted gross income has crossed the first Medicare line. This couple is 63, so this return sets the premium for 2028, the first year both are on Medicare, and the surcharge lands then on top of the income tax. The $150,000 row stays under it. That is the sizing decision in one table: the ceiling that binds is not always the bracket.
A method you can repeat every December
The conversion cannot be undone, so the margin matters. A conversion that lands a few thousand dollars under the ceiling wastes a little bracket. A conversion that lands one dollar over the Medicare line costs about $1,949 for that dollar. Aim under, not at.
Want the exact number for your return this year?
Free 30-minute call with Jim. Bring your numbers. You leave knowing where you stand.
Book my free callKeep going
Quick answers
- How much of my IRA should I convert to Roth each year?
- Up to the lowest ceiling that applies to you that year: the top of the bracket you are willing to pay, the Medicare IRMAA line measured two years out, the Social Security taxation zone if you are collecting, past 65 the income where the $6,000 senior deduction starts to phase out, and before 65 the marketplace premium-credit line if you buy your own health insurance. Add up everything else on the return, subtract your deductions, and the conversion is the gap between that and the ceiling, less a margin.
- How much room does a retired couple have in the 12% bracket in 2026?
- The 12% bracket ends at $100,800 of taxable income for a married couple. A couple drawing $40,000 from an IRA with nothing else on the return has $7,800 of taxable income after the $32,200 standard deduction, so $93,000 of conversion fills the bracket. The 22% bracket ends at $211,400, leaving $203,600 of room.
- Which ceiling do people hit by accident?
- The Medicare line. It is measured on modified adjusted gross income, not taxable income, it takes effect two years after the conversion, and it is a cliff: one dollar over the first 2026 line of $218,000 for a couple costs about $1,949 of Part B premium for the year. Size the conversion to stop under it with a margin.
Updated . Reviewed by Jim Swiech, CPA.
Educational and general in nature. Not tax, legal or investment advice, and not a recommendation to convert. Figures are 2026 federal amounts under the assumptions stated on this page; your return has more lines than any example. Go Beyond Tax is a brand of Swiech Consulting LLC.