What is IRMAA and how does it affect Medicare premiums?
IRMAA is the income-related monthly adjustment amount — an addition the law requires to Part B and Medicare prescription drug coverage costs for higher-income beneficiaries. It is not a separate plan, a tax or a penalty; it is a larger share of the same coverage.
It is measured on modified adjusted gross income, which for this purpose is adjusted gross income plus tax-exempt interest, taken from a tax return for an earlier year. That lag is why a premium can describe a year that no longer resembles your situation.
The published tables set one amount per band rather than a sliding scale, and the bands and amounts are set annually. The current year's figures are carried in this page's sources rather than written into the text, so they cannot go quietly out of date.
IRMAA is measured on an old year and charged in a later one
The adjustment for a given year is normally based on a tax return from an earlier year. That lag is the single most useful thing to understand about it, because it means the cost of an income decision arrives later than the decision.
It also means the premium someone is paying today may describe a year in which they were still working, still selling, or still realising gains.
The tables are bands, not a sliding scale
The published tables set one amount per band. Income that falls into a higher band carries that band's amount rather than a proportionate share of it.
This is why the arithmetic of a planning decision is about where a year's income lands, not only about how large it is.
What a general answer cannot settle
Enrolment requirements, payer order, the band that applies to a household, whether a request to revisit a determination will succeed, and the amount that may still be contributed to a health savings account are all individual determinations made by Social Security, Medicare, the plan or a tax professional on the facts and documents.
This page is written to help someone ask better questions of those parties and to see the connections between decisions. It does not make any of those determinations, and no figure here is calculated for a reader.
Reviewed by Bay Area Wealth Advisors. Last reviewed 2026-09-20. Educational information only — not individualized financial, tax or legal advice.