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IRMAA 2026: Medicare's income surcharge is a cliff, not a phase-in
IRMAA (the Income-Related Monthly Adjustment Amount) is the surcharge Medicare adds to Part B and Part D premiums for higher-income enrollees. It isn't a gradual phase-in: it's five tiers, and landing $1 over a threshold adds the full surcharge for that tier, not a prorated slice of it. The income that decides your IRMAA tier for a given year isn't that year's income at all -- it's your MAGI from two years before. That lag is why a Roth conversion or a QCD-vs-cash choice made this December can quietly set a Medicare premium two years out, long after the decision itself is forgotten.
The 2-year lookback
Your 2026 Medicare premiums are based on your modified adjusted gross income (MAGI: AGI plus tax-exempt interest) from your 2024 tax return. By the same pattern, income reported on your 2026 return sets your 2028 premiums. There's no way to undo it after the fact once the return is filed -- outside a handful of narrow appeal reasons (SSA calls them "life-changing events": marriage, divorce, death of a spouse, work stoppage, loss of income-producing property, and a few others), a high-income year is locked in for Medicare purposes two years later no matter what your income does in between.
The 2026 IRMAA tiers
These are the premiums and surcharges for 2026, from CMS's official November 14, 2025 announcement. The standard Part B premium with no surcharge is $202.90/month. Part D's IRMAA is a surcharge added on top of whatever your own Part D plan charges -- it isn't a total premium the way the Part B column is.
| MAGI, single | MAGI, married filing jointly | Part B surcharge | Part B total premium | Part D surcharge |
|---|---|---|---|---|
| $109,000 or less | $218,000 or less | $0.00 | $202.90 | $0.00 |
| $109,001 – $137,000 | $218,001 – $274,000 | $81.20 | $284.10 | $14.50 |
| $137,001 – $171,000 | $274,001 – $342,000 | $202.90 | $405.80 | $37.50 |
| $171,001 – $205,000 | $342,001 – $410,000 | $324.60 | $527.50 | $60.40 |
| $205,001 – $499,999 | $410,001 – $749,999 | $446.30 | $649.20 | $83.30 |
| $500,000 or more | $750,000 or more | $487.00 | $689.90 | $91.00 |
Run your own MAGI (from two years ago) through the IRMAA calculator to see your tier, both surcharges, and how much MAGI room is left before the next tier -- the number that matters if you're planning a conversion this year for premiums two years out.
Why it's a cliff, not a phase-in
Each tier applies to your entire MAGI once you're in it -- there's no blending at the edge. That makes the dollar right at a threshold enormously more expensive than the dollar right before it. A worked example, both at the same tier boundary ($137,000 for a single filer), two years apart in effect:
| 2024 MAGI (sets 2026 premiums) | Tier | Part B total premium | Part D surcharge | Combined monthly surcharge |
|---|---|---|---|---|
| $136,900 | 2nd tier ($109,001–$137,000) | $284.10 | $14.50 | $95.70 |
| $137,100 | 3rd tier ($137,001–$171,000) | $405.80 | $37.50 | $240.40 |
A $200 difference in 2024 MAGI -- $136,900 against $137,100, crossing the $137,000 line by just $100 -- raises the Part B premium by $121.70/month and the Part D surcharge by $23.00/month: $144.70 more a month, $1,736.40 more for the year, for one person on Medicare. Nothing about the person's health, coverage or Part D plan changed; $200 of extra MAGI, in the wrong direction, from two years earlier, is the entire cause. A married couple both on Medicare in the same tier would see this doubled, since each spouse's premium is set from the same joint MAGI.
How this connects to year-end decisions
Because of the 2-year lookback, the MAGI that matters for IRMAA right now is whatever your 2026 tax return will show -- which won't set a Medicare premium until 2028. That makes it easy to ignore in December, since nothing about it is due by December 31. But two of the moves already on this site's year-end tax moves checklist change this year's MAGI directly, and the IRMAA thresholds don't care why the income showed up:
- A Roth conversion is taxable income the year you do it, and it raises MAGI dollar for dollar. Sized to "fill the 12% bracket" using the income tax calculator, a conversion can still land MAGI just over an IRMAA threshold two years out even if it stays inside the tax bracket you were aiming for -- the tax bracket and the IRMAA tier are two different lines, and they don't fall in the same place. Check the result against the IRMAA table above, not just the tax brackets.
- Taking an RMD as cash and giving to charity, instead of a QCD, adds the full RMD to MAGI; a QCD of the same amount doesn't, because it never counts as income. The QCD calculator and the QCD vs. cash gift guide work the income-tax side of that choice; the IRMAA tier table above is the piece they leave out, and it can be the larger cost for someone already near a threshold.
- Both decisions interact with the pace you planned using the RMD calculator for the RMD itself: the distribution amount is fixed by the account balance and your age, but whether it adds to MAGI (cash) or doesn't (QCD) is a choice, and a conversion on top of it adds more MAGI on the same return.
The practical habit: before finalizing a conversion amount or a cash-vs-QCD choice in December, add the result to the rest of this year's MAGI and check it against the IRMAA table above, not just against your tax bracket. The 2028 thresholds will be adjusted for inflation and won't be identical to the 2026 ones above, but the tier structure and the cliff mechanics will work the same way -- the 2026 table is the clearest stand-in available until CMS publishes the 2028 numbers.
Every figure above comes from CMS's official 2026 Medicare Parts A & B premiums and deductibles announcement (November 14, 2025) and its companion 2026 Part D IRMAA amounts, cross-checked against CMS's published final notices. This is an illustration of the mechanics, not a projection of your own premium or tax advice -- appeals, state Medicaid programs that cover Part B premiums, and your own MAGI history all affect the real number.