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One dollar over the line costs $1,148 a year. Know where the line is.
Medicare charges higher-income beneficiaries an Income-Related Monthly Adjustment Amount on top of Part B and Part D premiums — and it is a cliff, not a phase-in: $1 over a threshold triggers the full tier surcharge for the entire year. For 2026, the standard Part B premium is $202.90/month and surcharges start above $109,000 MAGI (single) or $218,000 (married filing jointly), based on your 2024 tax return. This calculator shows your exact tier, the per-person and household cost, and your headroom before the next cliff.
Anyone approaching 65 — or doing Roth conversions near it — uses it to find the cliff edges: IRMAA surcharges trigger on $1 over a threshold and are assessed per person, so one oversized conversion can cost a couple $1,148–$13,872 in a single year two years later.
For single filers: standard premium up to $109,000 MAGI, then tiers at $137,000, $171,000, $205,000, and $500,000. Joint filers: $218,000, $274,000, $342,000, $410,000, and $750,000. Total Part B premiums run $202.90 to $689.90 per month; Part D surcharges add $0 to $91.00. Crossing the first threshold by $1 costs $95.70/month — $1,148.40/year — per person.
Social Security sets IRMAA from the most recent IRS data available, which runs two years behind: 2026 premiums use your 2024 MAGI. If your income has since dropped because of a qualifying life-changing event — retirement, divorce, death of a spouse, loss of pension — file Form SSA-44 to have premiums based on more recent income. A voluntary Roth conversion is not a qualifying event.
A Roth conversion counts fully in MAGI, so a large conversion can push you into a higher tier two years later — for one year, then it resets. The planning move is to size conversions to fill up to, but not over, the next threshold: a single filer at $95,000 MAGI has $14,000 of room before the first cliff. Income at 63 sets your premiums at 65, so the conversion window before 63 carries no IRMAA cost at all.