What IRMAA is. Medicare Part B has a standard monthly premium — $202.90 in 2026 — that most people pay. If your income is above the first threshold, you pay that standard premium plus a surcharge, and a second surcharge on top of your Part D drug plan. The surcharges climb through five tiers. The Social Security Administration determines your tier from IRS data and mails you a determination notice; the Part B piece is usually deducted straight from your Social Security check.
The 2026 brackets (based on 2024 MAGI). The first tier begins at $109,000 for single filers and $218,000 for married filing jointly. The tiers are multiples of the standard premium (1.4×, 2.0×, 2.6×, 3.2×, 3.4×), so the total Part B premium climbs from $202.90 to about $689.90 at the top, with a matching Part D surcharge layered on:
| 2024 MAGI — Single | 2024 MAGI — Joint | Total Part B / mo | Part D surcharge / mo |
|---|---|---|---|
| ≤ $109,000 | ≤ $218,000 | $202.90 | $0 |
| $109,001 – $137,000 | $218,001 – $274,000 | ~$284.10 | ~$14.50 |
| $137,001 – $171,000 | $274,001 – $342,000 | ~$405.80 | ~$37.50 |
| $171,001 – $205,000 | $342,001 – $410,000 | ~$527.50 | ~$60.40 |
| $205,001 – $500,000 | $410,001 – $750,000 | ~$649.30 | ~$83.30 |
| > $500,000 | > $750,000 | ~$689.90 | ~$91.00 |
(2026 figures. Part B totals are CMS-set and rounded here; the first four thresholds are inflation-indexed each year, while the top tier is currently frozen. Married-filing-separately has its own, harsher schedule. Reconfirm exact cents against the CMS "2026 Medicare Parts A & B Premiums" release before acting.)
Why the cliff is the whole story. IRMAA does not work like an income-tax bracket, where only the dollars above the line are taxed at the higher rate. It works like a toll gate: cross the line by a single dollar and you owe the full surcharge for that tier on every premium dollar, all year.
The $1 cliff
A single retiree has 2024 MAGI of exactly $137,000. She sits at the top of Tier 1 and pays about $284.10/month for Part B. Her twin brother has MAGI of $137,001 — one dollar more — which lands him in Tier 2 at about $405.80/month. That single dollar costs him roughly $122 more per month on Part B alone, about $1,460 for the year, plus a higher Part D surcharge on top. Same income to the penny, wildly different Medicare bill.
The married couple
A married couple's 2024 MAGI crosses from $218,000 to $218,001, moving into Tier 1. Each spouse now pays about $81 more per month for Part B, plus a Part D surcharge. Across both people and both parts, that's roughly $2,300 for the year — triggered by a single dollar of extra income two years earlier.
Where the surprise income comes from. IRMAA uses MAGI = AGI + tax-exempt interest. That add-back catches people who thought their muni-bond income was invisible. The usual culprits that push retirees over a line are large one-time events: a Roth conversion that was otherwise smart, a home sale with a big gain, a mutual-fund capital-gains distribution, or a required minimum distribution arriving at exactly the wrong time.
The two-year lag is a weapon, not just a trap. Because 2026 premiums key off 2024 income, you can see the surcharge coming and steer. Any move you make this year to lower MAGI shows up in your premiums two years from now. That makes the low-income gap years — after work stops but before RMDs and Social Security ramp up — the prime window to do Roth conversions up to, but not over, the next IRMAA threshold.
Bracket-filling without falling off
A single 63-year-old in a gap year has $70,000 of MAGI and wants to convert traditional IRA money to Roth. Keeping total MAGI at or below $109,000, she can convert roughly $39,000 with no IRMAA consequence. Convert enough to reach $109,001 and she'd trigger Tier 1 two years later. The move is to convert to the line, not over it, and repeat across several gap years.
The safety valve: SSA-44. If your income has genuinely dropped because of a qualifying life-changing event — work stoppage/retirement, marriage, divorce, death of a spouse, loss of a pension — you can file Form SSA-44 to ask the SSA to use your current, lower income instead of the two-year-old return. Someone who retired in 2025 but whose 2024 return still shows full employment income can appeal their 2026 IRMAA with 2025 documentation. Approval rates for legitimate events are high, but you have to know to ask.