Roth Conversion and IRMAA: A 2026-to-2028 Medicare Cost Worksheet

A Roth conversion completed in 2026 generally enters the 2026 federal return and may affect 2028 Medicare IRMAA under the normal two-year lookback. As of August 23, 2026, the 2028 IRMAA thresholds and premium amounts have not been published. Size a conversion with a tax-year-to-premium-year worksheet and multiple future threshold scenarios, not by treating the published 2026 IRMAA table as a promised 2028 ceiling.

This guide is a coordination worksheet. It does not reproduce the full 2026 IRMAA table, calculate an optimal Roth conversion, predict 2028 premiums, prepare a tax return, determine SSA-44 eligibility, or recommend crossing or avoiding a Medicare tier.

How does a 2026 conversion reach a 2028 Medicare premium?

SSA generally uses tax-return information from two years before the premium year. If the expected return is unavailable, SSA can use older information and later update the determination. The worksheet should therefore store both the expected tax year and the tax year actually shown in the notice.

The relationship belongs to calendar tax years, not to one universal birthday rule. A conversion at age 63 often receives attention because it may map to an age-65 Medicare year, but birth month, enrollment timing, delayed coverage, spouse ages, filing dates, and data availability can change the result.

How is this worksheet different from an IRMAA table or conversion calculator?

The 2026 IRMAA guide owns the published 2026 thresholds, Part B and Part D amounts, married-filing-separately rules, notices, and appeal mechanics. Those 2026 amounts apply to 2026 premiums using the applicable earlier return; they are not the official 2028 schedule.

The Roth conversion timing guide explains how to build candidate conversion ranges from a complete 2026 tax projection. It covers IRA basis, RMDs, taxable Social Security, preferential-rate income, deductions, credits, state tax, payments, and execution.

This page connects those two decisions. It maps each candidate conversion from the tax return to a later premium-year scenario, calculates exposure by enrolled person and month, and preserves the evidence needed when the actual Medicare notice arrives.

How does a Roth conversion change IRMAA MAGI?

For IRMAA, MAGI generally means adjusted gross income from the federal return plus tax-exempt interest. It is not taxable income after the standard or itemized deduction, gross cash received, or the amount transferred to the Roth account.

Build the estimate in this order:

1. Project AGI without the candidate conversion.
2. Calculate the taxable conversion after IRA basis and aggregation rules.
3. Recalculate income items that respond to the conversion, including the taxable portion of Social Security.
4. Complete the federal AGI calculation rather than adding labels from account statements.
5. Add tax-exempt interest to obtain projected IRMAA MAGI.
6. Preserve a range for income, deductions above AGI, basis, gains, losses, business results, and other facts that remain uncertain.

A gross $50,000 transfer is not necessarily a $50,000 taxable conversion. Nondeductible basis is generally allocated under the pro-rata rules across the owner's traditional, SEP, and SIMPLE IRAs. Form 8606 and year-end account values matter. Spouses do not combine IRA basis; each person's IRA and Form 8606 history is separate.

An RMD is not eligible for rollover or conversion. A person who owes an RMD generally must distribute the required amount before treating later eligible dollars as a conversion. The Roth conversion and RMD guide preserves that ordering.

What should each candidate scenario contain?

The rows must use the same market date, return assumptions, spending, filing status, account values, and future horizon. Changing assumptions only in the preferred case makes the premium comparison unreliable.

Record a range instead of one exact candidate. Earlier in the year, income and investment results are less complete. Near year-end, the projection is more informed but custodian-processing risk is higher. Preserve a buffer for dividends, gains, fund distributions, Social Security adjustments, business income, and transactions that have not posted.

How should unknown 2028 IRMAA thresholds be modeled?

Do not copy the 2026 threshold into the 2028 column and label it official. Until CMS and SSA publish the 2028 amounts, create clearly labeled sensitivity cases. A useful worksheet can include a lower-threshold case, a planning reference case, and a higher-threshold case without claiming that any one will become law.

For each case, store the assumed filing-status table, threshold, Part B adjustment, Part D adjustment, publication status, and date reviewed. Replace the assumptions when the official 2028 schedule is released. Keep the earlier version so the household can see which information was available when the 2026 decision was made.

Current published tiers can help show how the mechanism works, but they are not a promise about inflation adjustments, legislation, Medicare premiums, or future filing-status tables. The decision should remain workable when the final threshold differs from the planning reference.

How should a couple calculate IRMAA exposure?

IRMAA is assessed per Medicare beneficiary. A joint return supplies one MAGI figure, but the premium calculation still depends on which spouse is enrolled in Part B, Part D, or both and for which months. Do not automatically double a household surcharge.

Use one row per person and coverage type:

• Medicare enrollment date and months covered in the premium year.
• Part B status, including any change or termination.
• Part D or Medicare Advantage drug coverage and the separate Part D adjustment.
• Filing status and whether the special married-filing-separately table applies.
• Expected withholding from Social Security or direct billing method.
• Any midyear determination, correction, or life-changing-event request.

A spouse who is not enrolled does not owe an IRMAA merely because the joint return exceeds a threshold. A spouse who enrolls later can have fewer affected months than a full-year estimate. The actual notice and coverage record control.

Does crossing a tier mean the conversion should be reduced?

No. IRMAA changes in tiers, so a small MAGI increase can create a discrete premium increase. That is a cost to measure, not an automatic instruction to stop below a line. Reducing a conversion can increase later traditional-account balances, future RMDs, survivor filing-status exposure, or beneficiary taxable distributions. Increasing a conversion can raise current tax, consume cash, change subsidies, or create more later Medicare cost.

The opposite shortcut is also unreliable: do not convert automatically to the top of a tier after crossing it. The future tier is not yet known, and every additional dollar can affect current federal and state tax, taxable Social Security, capital-gain stacking, deductions, credits, and investment exposure.

Compare total household outcomes under identical scenarios. Include:

• 2026 federal and state tax.
• Marketplace premium tax credits when either spouse is not yet on Medicare.
• Tax-payment source and assets removed from the portfolio.
• Estimated 2028 Part B and Part D adjustments by person and month.
• Future RMDs and traditional, Roth, and taxable account balances.
• Survivor filing status, beneficiary goals, and uncertainty.

One premium-year estimate is not necessarily the whole IRMAA effect. Conversions or other income in several tax years can map to several later premium years, and a later determination can revise billed amounts.

Is age 63 the deadline for avoiding IRMAA?

No. Age 63 is a shorthand derived from a common age-65 enrollment and two-year lookback, not a statutory conversion deadline. The worksheet should map the actual conversion tax year to the actual premium year for each person.

A conversion before Medicare enrollment may have no IRMAA effect for a person who is not enrolled in the mapped premium year, but it can still affect federal and state tax, Marketplace coverage, Social Security taxation, cash, and future balances. A conversion after enrollment can still be reasonable when the complete comparison supports it.

Do not front-load conversions solely because a birthday is approaching. First confirm account basis, RMD status, filing status, income sources, insurance coverage, tax-payment assets, future spending, and the ability to absorb a different threshold than projected.

What must be completed in the 2026 conversion year?

A Roth conversion is generally reported for the calendar year in which the distribution and conversion are completed. An IRA contribution deadline does not extend the conversion deadline. Custodian cutoff dates can be earlier than December 31, and an instruction submitted on the last business day may not complete in time.

Confirm the receiving Roth account, eligible assets, direct-transfer method, withholding election, processing date, and transaction confirmation. Tax withheld from a distribution is money not converted; it can also create an additional-tax issue when the owner is under age 59 1/2 and no exception applies.

A conversion completed after 2017 generally cannot be recharacterized back to a traditional IRA. Update withholding or estimated payments using current rules instead of waiting for the Medicare bill two years later. Keep Forms 1099-R, 5498, 8606, account statements, basis history, payment confirmations, and the final return with the worksheet.

The year-end checklist separates transaction, contribution, and estimated-payment deadlines.

What should happen when the IRMAA notice arrives?

1. Confirm the premium year and tax year SSA used.
2. Match the filing status, AGI, and tax-exempt interest to the filed or amended return.
3. Compare the notice with the official threshold table for that premium year.
4. Check enrollment by person, Part B, Part D, and affected months.
5. Identify whether the issue is correct old data, unavailable newer data, incorrect IRS data, or a listed life-changing event.
6. Follow the notice's reconsideration or new-determination instructions and retain proof of submission.
7. Update the worksheet with the actual determination and later corrections.

Form SSA-44 is not a Roth-conversion cancellation form. It supports a request for a new initial determination after a listed life-changing event and a documented reduction in MAGI. The listed events include marriage, divorce or annulment, death of a spouse, work stoppage, work reduction, involuntary loss of income-producing property, loss of certain pension income, and an employer settlement payment.

A voluntary conversion is not itself a listed life-changing event. If a separate qualifying event occurs, the newer or estimated MAGI used in the request must still include taxable conversions and other income that belong in that year. Incorrect IRS data, an amended return, or a disagreement without a listed event follows the applicable notice and reconsideration process instead.

A reusable Roth conversion and IRMAA workflow

1. Create one row for each conversion tax year and its normally linked premium year.
2. Project AGI without the conversion, then calculate taxable conversion after basis and RMD rules.
3. Recalculate the complete return and add tax-exempt interest for IRMAA MAGI.
4. Run no-conversion, lower, middle, and upper candidate scenarios with identical assumptions.
5. Add Marketplace, state tax, tax payments, liquidity, future RMD, survivor, and beneficiary effects.
6. Create alternative future threshold and premium cases until official amounts exist.
7. Calculate Part B and Part D exposure separately for each person and month enrolled.
8. Confirm custodian timing and complete the conversion only after the payment plan is funded.
9. Reconcile the return, Forms 8606 and 1099-R, and account records after filing.
10. When the Medicare notice arrives, replace projections with the tax year, table, enrollment, and determination actually used.

The RetireStride methodology explains why the public retirement calculator does not estimate an individual's Roth conversion or IRMAA charge. A future saved worksheet should version tax years, premium years, filing-status tables, enrollment by person, official-versus-assumed values, and calculation evidence rather than storing one generic surcharge.

RetireStride provides educational retirement-planning information, not individualized tax, legal, Medicare, insurance, investment, or appeal advice. Tax returns, IRA basis, conversion processing, future thresholds, Medicare enrollment, SSA determinations, state rules, subsidies, and household needs can change the result. Confirm an actual transaction and notice with current IRS, CMS, SSA, Medicare, and qualified professional guidance.

Practical next step. Put four dates on one page: the proposed conversion date, the 2026 return filing date, each spouse's Medicare enrollment date, and the expected 2028 determination. Then add one row for every income source that can change 2026 AGI or tax-exempt interest.