Medicare IRMAA calculator (2026)

IRMAA — the Income-Related Monthly Adjustment Amount — is the surcharge Medicare adds to your Part B and Part D premiums when your income is above a threshold. Two things make it unusually easy to walk into: it is a cliff, so one dollar over a threshold costs the entire step, and it is based on your tax return from two years earlier, so the damage is done long before the bill arrives. Here are the 2026 brackets, then what a Roth conversion in your early sixties actually costs you at 65.

2026 IRMAA brackets (Part B + Part D surcharges)

Thresholds apply to the MAGI on the return filed two years before the premium year, and the surcharge is charged per person on Medicare — a married couple who are both enrolled pay it twice:

These are the surcharges only — the standard Part B premium everyone pays sits underneath them and belongs in your general healthcare budget. Thresholds are inflation-indexed each year except the top tier ($500,000 single / $750,000 joint), which is frozen by statute and therefore catches more people every year.

What a Roth conversion at 63 costs at 65

This is the version of the question that matters, and the one a MAGI-entry box can't answer: you don't know your future MAGI, you know your withdrawal plan. Coastline projects the MAGI each year of your plan produces and then applies the two-year lookback to it, the same way CMS does. A married couple retiring at 63 with a $1,400,000 traditional balance, converting once:

Three things worth reading off that table. The surcharge is $2,297 on a $250,000 conversion — real money, but small next to the $37,468 of income tax the conversion costs anyway, and far smaller than the lifetime tax a well-timed ladder can save. It is charged for one year only: by 66 the lookback has moved on to a normal-income year and the surcharge returns to $0. And it is a step function — the same conversion sized $1 lower could sit in the tier below and cost nothing extra.

A single filer sees the same mechanics at half the thresholds: a $125,000 conversion at 63 lands in tier 1 and costs $1,148 at 65, charged once, for one beneficiary.

Why the two-year lookback is the whole problem

• Your 2026 premium is set by your 2024 income. The years that decide your first Medicare premiums are ages 63 and 64 — exactly the years most retirement plans schedule big Roth conversions, business sales, or a house sale.
• One-time events count. Selling a rental or downsizing a home can produce a single huge MAGI year and a surcharge two years later. Coastline deliberately includes realized home and rental sale gains in the MAGI it carries forward, because leaving them out made a multi-million-dollar downsizing read as a $0 surcharge.
• Life-changing events can be appealed. Retirement itself is one of them. If your income dropped because you stopped working, form SSA-44 asks Social Security to use your current income instead of the two-year-old figure — a step many retirees never learn about.
• It repeats annually. IRMAA is recalculated every year from the return two years prior, so a single spike costs one year, and a sustained high income costs every year.

Planning around it

• Convert before 63, or accept the surcharge deliberately. Conversions at 60–62 never touch a Medicare premium. From 63 on, every conversion has a premium consequence two years out.
• Size conversions to the threshold, not to the bracket. The income-tax bracket and the IRMAA tier are different lines in different places. A conversion that fits neatly inside the 22% bracket can still cross an IRMAA threshold.
• Remember it is per person. For a couple both on Medicare the surcharge doubles — $2,297 at tier 1 — which also means a much younger spouse delays half the cost until they enrol.
• Weigh it against what conversions save. A one-year $2,297 surcharge is often a fair price for permanently smaller required distributions. The mistake is not paying IRMAA; it is paying it without knowing.

Why Coastline's version is different

Most free calculators hand you a single headline number with the assumptions hidden. Coastline is built the opposite way:

• Real tax math, not a flat rate. It applies federal and state income tax, long-term capital-gains rules, and account-by-account treatment (taxable, traditional, Roth) — in both your working years and retirement.
• The whole journey. It models accumulation (saving and investing) and drawdown (spending it down), so you see how the plan connects end to end, not just one half.
• The math is shown. Every figure has a click-through breakdown of how it was computed — a level of transparency even paid tools rarely expose.
• US and Canada. It natively handles Canadian plans (RRSP, TFSA, CPP, OAS) alongside US accounts, which most calculators ignore.
• Free, no signup. No account, no email, no account-linking. Your inputs run the projection and are then discarded.

Educational, not tax advice. Thresholds and premiums are the 2026 figures from the CMS announcement; the projection indexes them with the plan's general inflation except the statutorily frozen top tier, and charges the surcharge per enrolled beneficiary. Two documented simplifications: premiums are grown at general inflation rather than medical inflation (which historically runs faster, so later years are understated), and the first two years of a plan have no full two-year history — the projection falls back to a one-year lookback in year two and charges nothing in year one, and says which it used. Surcharge figures above are shown in today's dollars. Verify current-year brackets at medicare.gov before acting.

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