What is IRMAA, and how does it work?

The tiers step. One dollar over a threshold triggers the whole tier’s surcharge. There is no phase-in and no marginal rate. Someone $1 above the first 2026 line pays $1,148.40 more across the year than someone a dollar below it.

The return that set it is already filed. By the time a surcharge appears, the return it was calculated from is two years old. Income earned in the current year sets the premium two years later.

A single year can trigger it. A Roth conversion, a property sale, an inherited IRA, a large capital gain or a lump-sum pension payment can each raise MAGI above a threshold for one year. The surcharge applies two years later for twelve months, after which SSA uses the next return.

The range. At the top tier in 2026, IRMAA adds $6936.00 a year per person on top of standard premiums. At the first tier it is $1148.40. For a couple, both spouses pay it separately.

IRMAA uses modified adjusted gross income: your adjusted gross income plus tax-exempt interest. In practice that means it counts most of what you might not expect it to.

Social Security sends an Initial IRMAA Determination Notice when a surcharge applies, normally toward the end of the year before it starts. It names the tax year used and the bracket it put you in — worth checking, because the wrong year is one of the more common errors.

If you already receive Social Security, the surcharge is deducted from that payment alongside your standard premium. If you are not yet claiming, Medicare bills you directly. Part D IRMAA is paid to Medicare, not to your drug plan, even though the plan premium itself goes to the insurer.

See medicare.gov on the determination notice.

Sometimes. If your income has fallen because of a life-changing event — retirement or reduced work hours, the death of a spouse, marriage or divorce, loss of a pension, loss of income-producing property — you can ask Social Security to use a more recent year instead of the two-year-old return, using Form SSA-44.

Simply having a high-income year does not qualify. The rule is aimed at circumstances that changed your income going forward, not at one-off gains. A Roth conversion or a property sale is not a life-changing event, however much it raised your MAGI.

Otherwise the lever is timing: managing which year income lands in, so it does not push you over a line. We have worked through what changes IRMAA MAGI and what does not, with the cost of crossing each threshold. Late enrollment is a different surcharge on the same bill: see the Part D late enrollment penalty. At the other end of the income range, the Medicare Savings Programs pay the Part B premium outright.