IRMAA cliffs: the Medicare surcharge that arrives two years later
A single dollar over an income threshold can raise your Medicare premiums by hundreds — and the bill shows up two years after the income. Here's how the tiers work and where the real cliffs sit.
Most retirees plan taxes against one clock: the current year. IRMAA runs on a second clock that's two years behind.
IRMAA — the Income-Related Monthly Adjustment Amount — is a surcharge on top of the standard Medicare Part B and Part D premiums. It's based on your modified adjusted gross income from two years earlier. Your 2026 premiums, for example, are set by your 2024 tax return.
The part that surprises people
IRMAA is a cliff, not a phase-in. Cross a threshold by one dollar and the surcharge applies to the whole year's premiums. There's no proration and no gradual ramp.
That creates a familiar pattern: a large Roth conversion or an unplanned capital gain doesn't just cost income tax in the year you take it — it can quietly raise your Medicare premiums two years later.
Where the cliffs sit
The thresholds are indexed to inflation each year and differ by filing status. The mechanics matter more than today's exact numbers:
- Both spouses on Medicare — the household surcharge is roughly double.
- The first tier kicks in well below the top brackets, so IRMAA often binds before the next federal bracket does.
- Tax-exempt interest counts toward MAGI even though it's untaxed.
That last point trips people up constantly. Municipal bond interest is untaxed for income-tax purposes but can still push you over an IRMAA threshold.
Planning around it
The practical takeaway is that "headroom" isn't just about brackets. When you're deciding how much to withdraw or convert, the binding constraint is often the nearest cliff — and there can be several:
- The next federal tax bracket
- The ACA premium tax credit cliff (before age 65)
- An IRMAA tier (age 63 onward, because of the two-year lookback)
- The Social Security tax torpedo
RetireTaxGuide's current-year tax planner shows all of these at once, so you can see which one actually limits your next dollar — and what that dollar really costs once you cross a line.
This is educational information, not tax advice. Thresholds change annually; confirm the current figures at Medicare.gov and with a qualified professional.