A $600K MAGI Pushes Medicare to $628.90/Month — $6,356/Year in IRMAA Surcharges

$1 over the line costs you the whole tier

We ran a single filer’s MAGI from $105,000 up to $106,001 through the calculator. At $105,000, Part B costs $185.00/month — the base premium, no surcharge. At $106,001, just $1,001 more, Part B jumps to $259.00/month, a $74/month, $888/year increase. That’s the defining feature of IRMAA: it isn’t a progressive bracket like income tax, where only the dollars over the line get taxed at the higher rate. It’s a cliff — cross it by any amount, and the entire premium moves to the higher tier for the full year.

How the math works

Your MAGI from two years prior is checked against five brackets (six including the base tier) for your filing status. Each bracket sets a fixed total Part B premium and a fixed Part D surcharge — for 2025, a single filer’s top tier ($500,001+ MAGI) pays $628.90/month for Part B (a $443.90 surcharge over the $185.00 base) plus an $85.80/month Part D surcharge, for $6,356.40/year in total IRMAA cost.

What this tool doesn’t model: the married-filing-separately bracket structure (much narrower — most of the “married” thresholds don’t apply), the SSA appeals process for a “life-changing event” (job loss, divorce, death of a spouse) that can get a recent, high MAGI year excluded, and any year-over-year bracket inflation adjustment beyond the current 2025 figures baked into this calculator.

Math runs locally. Inputs never leave your browser. Source on github.

Where this calculator doesn’t apply

• You’re not on Medicare yet. IRMAA only applies once you’re enrolled in Medicare Part B/D — typically starting at 65. A large income year well before then has no IRMAA consequence at all (though it still affects that year’s regular income tax).
• You just had a life-changing event. Retirement, job loss, divorce, or the death of a spouse can qualify you for an SSA appeal (Form SSA-44) that uses your current, lower expected income instead of the two-years-prior MAGI this tool assumes.
• You file married filing separately. That status has a much narrower bracket structure — most of the wide “married filing jointly” thresholds don’t apply, and even modest MAGI can hit the top tier.
• Your MAGI is unusually volatile year to year. A one-time capital gain or Roth conversion spikes IRMAA for exactly one premium year (two years later), then reverts — this tool shows a single year’s snapshot, not a multi-year projection.

What to actually do with this number

1. Check where your current MAGI sits and how close it is to the next tier’s threshold.
2. If you’re close to a threshold and control the timing (a Roth conversion, a large capital gain), consider spreading it across years instead of one lump year.
3. Look at Qualified Charitable Distributions if you’re 70½+ and charitably inclined — they reduce MAGI directly instead of going through a deduction.
4. If a life-changing event just dropped your income, file SSA-44 rather than accepting the two-years-prior MAGI default.
5. Rerun this calculator each year IRMAA thresholds are updated — they typically rise slightly with inflation.