Roth Conversion Tax-Bracket & IRMAA Calculator

Federal ordinary-income tax brackets work in layers. A conversion does not cause every dollar on the return to be taxed at the highest bracket reached. Instead, taxable income fills the lower layers first, and only the dollars above each ceiling enter the next rate. The calculator uses the official 2026 rate schedules for Single, Married filing jointly, Head of household, and Married filing separately. [1]

If taxable income before conversion is $100,000 for a Single filer and the taxable conversion is $20,000, the first $5,700 of that conversion fits below the $105,700 ceiling and is modeled at 22%. The remaining $14,300 enters the 24% layer. That allocation is more informative than multiplying all $20,000 by 24%.

The input is intentionally “estimated taxable ordinary income.” Gross income and adjusted gross income are different measures, and qualified dividends or long-term capital gains can require a different calculation. A tax projection is usually a better source for this input than a rough guess based on salary.

The engine calculates simplified ordinary federal income tax twice. First, it applies the 2026 brackets to taxable ordinary income before conversion. Second, it adds the modeled taxable conversion and calculates the schedule again. The difference is the estimated incremental federal tax attributable to this isolated model.

Incremental modeled federal tax = ordinary tax after conversion − ordinary tax before conversion. The effective modeled rate divides that difference by the taxable conversion amount. This approach captures a conversion that fills more than one bracket while avoiding the false assumption that one marginal rate applies to everything.

The result is not a complete federal return. It excludes capital-gain rates, the net investment income tax, alternative minimum tax, credits, qualified business income, state tax, Social Security taxation changes, additional Medicare tax, self-employment tax, penalties, and estimated-payment calculations. Those omissions can materially change an actual result.

The taxable portion of a conversion generally increases adjusted gross income. For Medicare IRMAA, MAGI generally means AGI plus tax-exempt interest. That is why the planning mode adds entered pre-conversion AGI, the taxable conversion, and tax-exempt interest. It is a simplified relationship, not a reconstruction of Form 1040. [6]

Medicare generally uses tax information from two years before the premium year. A 2026 conversion would therefore ordinarily be relevant to 2028 premiums. The 2028 thresholds and premiums are not known, so this calculator does not produce a 2028 surcharge. It compares projected 2026 MAGI with published 2026 thresholds only as a current reference.

The separate actual-premium mode uses 2024 MAGI to look up the published 2026 Part B and Part D adjustments. It does not add the proposed 2026 conversion. CMS publishes the standard 2026 Part B premium of $202.90 along with the income-related tables; ordinary Part D plan premiums are separate. SSA makes the official determination. [5]

A Roth conversion generally does not use the same annual dollar limit that applies to a regular Roth IRA contribution. That does not make every balance available or every amount consequence-free. An employer plan may restrict distributions, an RMD cannot be converted, and eligible account value still sets an operational boundary.

The calculator’s “modeled room” output answers a narrow arithmetic question: how much space exists between entered taxable income and a selected 2026 bracket ceiling. It does not identify a recommended amount. Capital gains, deductions, credits, business income, Social Security, Medicare, state tax, cash available for tax, and future expected income can all change the planning range.

Comparing several partial Roth conversion scenarios can expose how the marginal layers change. The broader conversion-amount guide explains why bracket room is only one factor.

The gross conversion is the total amount moved. The taxable amount may be smaller when valid after-tax basis is present. This tool subtracts the user’s expected nontaxable portion from the gross amount, never below zero. It does not calculate basis.

For traditional, SEP, and SIMPLE IRAs, Form 8606 generally applies pro-rata rules across the applicable IRA balances. A person usually cannot identify one account as “the after-tax IRA” and assume that its conversion is entirely tax-free. Prior Forms 8606, year-end values, distributions, and conversions can all matter. [2]

Use the field only when an estimated nontaxable amount has already been developed from appropriate records. For more detail, review how basis changes a conversion or the IRA basis FAQ.

An eligible pre-tax employer-plan distribution rolled to a Roth IRA generally creates taxable income. A direct rollover can avoid the mandatory 20% withholding that generally applies when a taxable eligible rollover distribution is paid directly to the participant, but it does not avoid conversion tax. [3]

Plan rules determine whether a distribution is available. Former-employer money is often eligible for distribution, while a current-employer plan may limit in-service access. Roth, pre-tax, and after-tax sources can require separate instructions. The account selector changes the educational notice, not the tax-bracket math.

Read the canonical 401(k)-to-Roth IRA rollover guide before treating a workplace balance like an IRA. Payment timing is a separate issue covered in how to pay Roth conversion taxes.