A Roth conversion can create two bills. The first arrives at tax time. The second may not show up until two years later, when Medicare recalculates what you owe for Part B and Part D.
This guide owns one practical job: estimating how much Roth conversion room you have this year and comparing several conversion amounts before you act.
The calculation starts with projected IRMAA MAGI, identifies the next Medicare threshold, subtracts a realistic safety buffer, and then tests amounts below and inside the next tier.
If your real question is whether deliberately paying IRMAA can still be worthwhile, that is a separate decision. The full break-even, future-RMD, and legacy analysis belongs in the Roth conversion and IRMAA tradeoff guide.
The Roth Conversion and IRMAA Decision Framework
- Calculate baseline IRMAA MAGI Estimate income before adding any Roth conversion.
- Find the next IRMAA threshold Use the current filing-status threshold.
- Calculate threshold room Subtract projected MAGI from the next threshold.
- Apply a safety buffer Allow room for gains, distributions, and estimation error.
- Compare several conversion amounts Model one below the line and at least one inside the next tier.
- Run the larger tradeoff analysis Only when deliberately crossing a tier is under consideration.
Key point: Room below a threshold is not automatically the optimal conversion amount.
Key Takeaways Ahead
What IRMAA is. And why Roth conversions can trigger it
IRMAA stands for Income-Related Monthly Adjustment Amount. It is an additional monthly amount some higher-income Medicare beneficiaries pay for Part B and Part D.
For 2026, the standard Medicare Part B premium is $202.90 per month. The first IRMAA range begins when modified adjusted gross income exceeds $109,000 for an individual return or $218,000 for a joint return. The first range adds $81.20 per month to Part B and $14.50 per month to Part D for each affected person. Higher ranges add more. [1]
IRMAA works in income ranges. Crossing a range boundary can cause the higher monthly amount to apply for the premium year, rather than applying only to the dollars above the boundary. That step-like design is why a modest amount of additional income can create a noticeably larger annual Medicare bill.
A Roth conversion has two prices
A Roth conversion moves money from a pretax retirement account, such as a traditional IRA, into a Roth IRA. The previously untaxed portion of the amount converted is generally included in gross income for the conversion year. [2]
That is the first price: current income tax.
The second price may arrive later. Medicare generally uses federal tax information from two years before the premium year. So a conversion completed in 2026 may affect Medicare premiums in 2028. [3]
The conversion happens now. The Medicare consequence arrives later. That timing gap is easy to underestimate.
How Roth conversions enter the IRMAA calculation
The IRMAA income formula
For IRMAA, modified adjusted gross income is generally a two-part number:
- Adjusted gross income The AGI reported on the federal tax return.
- Plus tax-exempt interest income For example, interest reported from municipal bonds.
A taxable Roth conversion increases AGI, so it can also increase the income Medicare uses for IRMAA.
Source: Social Security Administration POMS HI 01101.010. [4]
Your baseline may include pension income, taxable retirement-account withdrawals, required minimum distributions, interest, dividends, capital gains, rental or business income, the taxable portion of Social Security, tax-exempt interest, and unusual one-time income. Use the IRMAA Income Checker for a guided estimate, or review what income counts toward IRMAA MAGI before entering a conversion amount.
This is why “fill the tax bracket” can be incomplete advice. Taxable income and IRMAA MAGI are not the same number. A conversion can fit inside a tax bracket and still move a household into a higher Medicare income range.
The 2026 IRMAA price list
For the maintained annual reference and filing-status details, see the 2026 IRMAA brackets and Medicare surcharge guide.
2026 Medicare Part B and Part D IRMAA amounts
These are monthly amounts for individual and joint filers. Part D IRMAA is paid in addition to the person’s Part D plan premium.
On a phone, swipe horizontally to see every column.
| Individual MAGI | Joint MAGI | Part B IRMAA | Part D IRMAA |
|---|---|---|---|
| $109,000 or less | $218,000 or less | $0 | $0 |
| Above $109,000 through $137,000 | Above $218,000 through $274,000 | $81.20 | $14.50 |
| Above $137,000 through $171,000 | Above $274,000 through $342,000 | $202.90 | $37.50 |
| Above $171,000 through $205,000 | Above $342,000 through $410,000 | $324.60 | $60.40 |
| Above $205,000 and below $500,000 | Above $410,000 and below $750,000 | $446.30 | $83.30 |
| $500,000 or more | $750,000 or more | $487.00 | $91.00 |
Swipe or scroll horizontally to see the full table.
Source: Centers for Medicare & Medicaid Services. Effective for 2026 Medicare premiums.
The table is a price list, not a decision rule. Married-filing-separately beneficiaries who lived with a spouse during the year use a different table.
Effective for 2026 Medicare premiums. Source: CMS, November 14, 2025. [1]
Start with your baseline—not your desired conversion
The first useful calculation is projected IRMAA MAGI before the conversion.
Do not automatically use last year’s number. Retirement years can change quickly: wages stop, pensions begin, Social Security starts, a property is sold, an RMD begins, or a mutual fund distributes an unexpected gain.
Suppose a married couple projects:
- $70,000 of pension income
- $35,000 of taxable IRA withdrawals
- $12,000 of interest and dividends
- $18,000 of taxable capital gains
- $30,000 of taxable Social Security
- $5,000 of tax-exempt interest
Their projected IRMAA MAGI before conversion is $170,000. That leaves $48,000 before the first 2026 joint threshold of $218,000.
But $48,000 is not automatically the best conversion amount.
Find your room to the next IRMAA range
A practical estimate is:
Next IRMAA threshold, projected pre-conversion IRMAA MAGI, safety buffer
Using the same household:
$218,000 − $170,000 − $5,000 = $43,000 of estimated room.
The buffer matters. Investment income, year-end distributions, gains, tax-exempt interest, and the taxable portion of Social Security can all move. A voluntary conversion or asset sale can also create a delayed premium surprise, as explained in the one-time income spike and IRMAA guide.
This number estimates room before the next IRMAA line. It does not prove that stopping there produces the best lifetime result.
Estimate Your Roth Conversion Room
This estimates room before the next IRMAA range. It does not determine whether stopping below that range is the best long-term choice.
Price the next dollars converted
The all-in cost of an additional conversion can include:
- Federal income tax. Part of the conversion may remain in the current bracket or move into a higher one.
- State income tax. State treatment varies.
- Part B IRMAA. Add the annual adjustment for each affected person.
- Part D IRMAA. Add it for each affected person enrolled in Part D coverage.
- Additional taxable Social Security. A conversion can cause a larger portion of benefits to become taxable because Social Security taxation depends on combined income. The Social Security tax and IRMAA trap guide explains that interaction. [5]
- Other interactions. Capital-gain rates, net investment income tax, deductions, credits, and health-insurance subsidies can matter.
The stated tax bracket alone does not capture all of these costs.
Compare three conversion amounts around the first IRMAA tier
Consider a married couple already on Medicare with projected pre-conversion IRMAA MAGI of $200,000. Both spouses are assumed to be enrolled in Part B and Part D.
They are $18,000 below the first 2026 joint threshold.
Three Roth Conversion Scenarios to Compare
Scenario 1
Stay Below the Threshold
Convert only the estimated room remaining after applying the safety buffer.
Best for: Households prioritizing near-term Medicare-cost certainty.
Scenario 2
Enter the Next IRMAA Tier
Accept the first surcharge while completing a larger conversion.
Best for: Households that may capture meaningful long-term tax benefits inside the tier.
Scenario 3
Use More of the Tier
Once a tier is deliberately entered, compare whether a larger conversion captures more value before the next threshold.
Best for: Households that have completed the full tradeoff analysis.
Key point: The Medicare surcharge may remain the same throughout an income range, but the tax cost continues to rise with the conversion.
Illustration only. Assumes both spouses are enrolled in Part B and Part D and no other income changes.
A larger conversion is not automatically better. The income tax may be too high. More Social Security may become taxable. State tax may matter. The money used to pay the tax may lose investment value.
But the Medicare cost should be compared with the full benefit rather than treated as a line that must never be crossed.
Before you deliberately cross an IRMAA tier
Do not decide from the surcharge alone. This article calculates the size of the conversion and the Medicare tier it may reach. The separate tradeoff analysis calculates whether accepting that tier is actually worth it.
That page owns the pay-IRMAA-or-not decision. It is intentionally not duplicated here.
Timing is a separate decision from sizing
Many households have a lower-income window after work ends and before Social Security and RMDs fully begin. This page helps size a conversion within a selected year; it does not attempt to choose the best year in a multi-year plan.
For the retirement-to-Medicare timeline, age-60-to-63 considerations, and the two-year lookback, use the Roth conversion golden-window guide.
Households using Affordable Care Act coverage before Medicare also need to model premium-tax-credit effects.
Three mistakes that make the math unreliable
1. Filling the tax bracket without calculating IRMAA MAGI
Taxable income and IRMAA MAGI are not the same number. A conversion that fits inside a bracket can still cross a Medicare threshold.
2. Assuming the conversion can simply be appealed
SSA allows a new IRMAA determination after specified life-changing events, such as marriage, divorce, death of a spouse, work stoppage, or work reduction. A voluntary Roth conversion itself is not one of the listed events. Review the SSA-44 IRMAA appeal guide before assuming an appeal is available. [7]
Do not complete a conversion while assuming Form SSA-44 will erase the Medicare consequence. Also remember that Roth conversions made after 2017 generally cannot be recharacterized back to a traditional IRA. [8]
3. Using exact projections with no buffer
A plan that depends on landing within a few dollars of a threshold may not be a plan. It may be a wager.
Annual Roth Conversion Planning Checklist
- Estimate current-year adjusted gross income.
- Add projected tax-exempt interest.
- Confirm which household members will be subject to Medicare.
- Check the current IRMAA thresholds.
- Estimate room to the next threshold.
- Apply a realistic safety buffer.
- Model at least three conversion amounts.
- Recalculate taxable Social Security.
- Estimate federal and state tax.
- Review the full tradeoff before deliberately crossing a tier.
- Confirm final year-end income before executing the conversion.
The decision rule to remember
The best Roth conversion amount is not automatically the top of your tax bracket. It is not automatically one dollar below an IRMAA threshold either.
The better target is the amount at which the expected long-term value of converting the next dollars still exceeds the combined current tax, Medicare, Social Security, and uncertainty costs.
Before completing a year-end conversion, compare at least three amounts: one below the next IRMAA line, one inside the next tier, and one that reaches your chosen tax-bracket target. Use the IRMAA calculator to estimate the Medicare surcharge for each scenario.
The right answer may be different from all three. But that comparison will show you where the real tradeoff begins.
Educational note
This article is educational and does not provide individualized tax, investment, legal, or Medicare advice. Roth conversions can interact with tax basis, filing status, state law, Social Security taxation, capital gains, Medicare rules, and other parts of a household plan. Confirm current-year figures and your specific tax consequences before completing a conversion.
Sources
- Centers for Medicare & Medicaid Services, “2026 Medicare Parts A & B Premiums and Deductibles.”
- IRS Publication 590-A, Contributions to Individual Retirement Arrangements.
- Social Security Administration, Premiums: Rules for Higher-Income Beneficiaries.
- SSA POMS HI 01101.010, Modified Adjusted Gross Income.
- SSA, Must I pay taxes on Social Security benefits?
- SSA, Request to lower an IRMAA.
- IRS Topic 309, Roth IRA Contributions.
