United States · IRS 2026 rates · CMS IRMAA
Roth conversion bracket room.
Find how many dollars you can convert before the next federal bracket and before each Medicare IRMAA threshold, then see the tax on the amount you choose.
Convert up to the bracket line to stay at your current rate. IRMAA is a cliff on MAGI from two years earlier: $1 over a threshold raises the whole year's Part B and Part D premium for that tier.
Your inputs
Your 2026 room
How the calculation works
Taxable income = other income + conversion − deduction (never below zero). A conversion is added to gross income (26 U.S.C. 408A(d)(3)) and taxed at the ordinary rates. Bracket room = top of the bracket + deduction − other income: the conversion that lifts taxable income exactly to that line. Conversion tax = tax on taxable income with the conversion minus tax without it, using the 2026 schedules.
IRMAA room = threshold − MAGI before conversion. MAGI here is your income plus the conversion. A tier applies only when MAGI is above its lower limit, so converting exactly up to a limit stays in the lower tier. Surcharges are the 2026 CMS monthly amounts per person times 12, Part B plus Part D.
Two-year lookback
Medicare sets premiums from the tax return filed two years earlier. A 2026 conversion therefore affects 2028 premiums, and CMS publishes new thresholds each year. The 2026 thresholds used here are a proxy, not a forecast.
Worked example (fictional)
Single, $80,000 other income, 2026 standard deduction $16,100, taxable income $63,900. Room to the end of the 22% bracket: $105,700 + $16,100 − $80,000 = $41,800. Room before the first IRMAA line: $109,000 − $80,000 = $29,000. Converting $50,000 costs $11,164 federal tax and lifts MAGI to $130,000, tier 1: about $1,148 a year more in Part B and Part D per person at 2026 amounts.
2026 IRMAA thresholds (MAGI)
| Tier | Single | Joint | Part B + D extra, per month |
|---|---|---|---|
| 0 | up to $109,000 | up to $218,000 | $0.00 |
| 1 | to $137,000 | to $274,000 | $81.20 + $14.50 |
| 2 | to $171,000 | to $342,000 | $202.90 + $37.50 |
| 3 | to $205,000 | to $410,000 | $324.60 + $60.40 |
| 4 | under $500,000 | under $750,000 | $446.30 + $83.30 |
| 5 | $500,000 or more | $750,000 or more | $487.00 + $91.00 |
Married filing separately and living with a spouse: tier 0 up to $109,000, tier 4 amounts above that and below $391,000, tier 5 at $391,000 or more.
Not modelled: state tax, net investment income tax, credits, AMT, the pro-rata rule, the additional senior deduction, changes to taxable Social Security, other IRMAA-lowering events, and any growth projection. Converted amounts also start their own five-year clock for the 10% early-distribution tax (Pub. 590-B).
Official sources: IRS Rev. Proc. 2025-32 (2026 rate tables and standard deduction); CMS 2026 Medicare Part B premiums and IRMAA; IRS Pub. 590-B; IRS Pub. 590-A; 26 U.S.C. 408A. All opened October 2, 2026.
Frequently asked questions
Does a Roth conversion count toward IRMAA?
Yes. A conversion is included in gross income (26 U.S.C. 408A(d)(3)), so it raises adjusted gross income and therefore the MAGI that Medicare uses. Medicare looks at your tax return from two years earlier, so a 2026 conversion can raise your 2028 Part B and Part D premiums.
Is IRMAA a bracket or a cliff?
A cliff. Federal brackets tax only the dollars inside each bracket, but crossing an IRMAA threshold by even $1 moves your whole premium up a tier for the year. That is why the table shows the dollars you can convert before each line.
How much can I convert without moving up a federal bracket?
The number in the first table. It is the top of the bracket (taxable income) plus your deduction, minus your other income. Converting exactly that amount fills the bracket without spilling into the next rate.
Does a conversion at age 63 or 64 affect Medicare?
It can. MAGI from two years before sets the premium, so a conversion made at 63 can raise the premium in the first year you are on Medicare. Conversions made before 63 do not affect premiums after that point.
What does this calculator leave out?
State tax, the 3.8% net investment income tax, credits, AMT, the pro-rata rule for after-tax IRA money, the additional senior deduction, extra tax on Social Security benefits, and any growth projection. It assumes a pre-tax conversion.
Are the IRMAA thresholds for the year I convert?
Not exactly. The 2026 thresholds shown apply to 2024 income. CMS resets them each year, so the thresholds that apply to your 2026 conversion will be the 2028 figures. The 2026 amounts are used here as the best published proxy.
Not investment or tax advice
This is an educational estimate of federal tax and Medicare surcharge thresholds. It excludes state tax and growth projections. Confirm your plan with a qualified tax professional.