Example 1: conversion stays inside the standard tier
A single filer starts with estimated MAGI of $92,000 and expects a $12,000 taxable conversion. The comparison MAGI becomes $104,000, which remains below the 2026 individual threshold of $109,000. The published-table headroom is $5,000.
The $5,000 is not a recommended additional conversion. Interest, dividends, gains, taxable Social Security, and return adjustments can move final MAGI. A planning buffer can reduce the risk that an unexpected year-end item crosses the boundary.
Example 2: conversion crosses one tier
A single filer starts at $100,000 and enters a $30,000 taxable conversion. The comparison MAGI becomes $130,000, which is in the first 2026 IRMAA tier. For one enrollee, the published Part B and Part D additions total $95.70 per month, or $1,148.40 for a full year, before any Part D plan premium.
Example 3: two enrollees amplify the household cost
A married couple filing jointly has MAGI of $210,000 and both are enrolled in Medicare. A $20,000 taxable conversion moves the comparison MAGI to $230,000, above the 2026 joint standard-tier boundary of $218,000. Both enrollees can be subject to the income-related amounts, so the household's annual addition is twice the per-person amount.
A conversion made in 2026 generally affects 2028 Medicare premiums. The examples use 2026 thresholds only because 2028 thresholds and premiums are not yet official.
Taxable amount can differ from gross conversion
If a traditional IRA contains nondeductible basis, Form 8606 and the pro-rata rules determine the nontaxable and taxable portions across traditional, SEP, and SIMPLE IRAs. Do not assume a particular account's after-tax dollars can always be isolated for this input.
Compare more than IRMAA
The same conversion can change marginal income-tax brackets, taxable Social Security, deductions, credits, net investment income tax, and state tax. Future RMD reduction and estate planning may outweigh a temporary Medicare premium increase, or the opposite may be true. IRMAA is one measured consequence, not the decision rule.
Sources: IRS Publication 590-B, Form 8606 instructions, and CMS 2026 premium table.
Last reviewed August 16, 2026.