What the question involves
Medicare charges higher Part B and Part D premiums, the income-related monthly adjustment amount (IRMAA), when your modified adjusted gross income from 2 years earlier is above a threshold. For IRMAA that is adjusted gross income plus any tax-exempt interest; the untaxed part of Social Security does not count. For 2026 the first tier starts above $218,000 for a married couple filing jointly and $109,000 for a single filer, and each further tier ($274,000, $342,000, $410,000, $750,000 joint) costs more. The tiers are cliffs: one dollar over a threshold costs the whole step.
What this tool computes
On the average-market path of your plan, each year whose income will set a Medicare premium: which tier it falls in, how far above that tier’s threshold it is, and the room left before the next one. Roth conversions and required withdrawals are in the income, so you can see which of them pushes a year over.
Every answer is a real run of the full simulator, on 1,000 simulated market paths in your browser. Nothing you type is sent anywhere.
What it leaves out
The thresholds are shown in today’s dollars and assumed to rise with inflation. Income in your two most recent years before the plan starts, appeals and one-off income such as a home sale are not part of this quick version.
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This page explains how the rules work. It is not financial, tax or investment advice. Disclaimer