Income-Related Monthly Adjustment Amount (IRMAA)

IRMAA is the income-related monthly adjustment amount: an extra charge added to the Medicare Part B and Part D premiums of beneficiaries whose modified adjusted gross income exceeded a published threshold. The full name is Social Security's regulatory term rather than the statute's. The Medicare statute at 42 USC 1395r calls it simply a "monthly adjustment amount" under a heading about reducing the premium subsidy based on income, and the Part D provision at 42 USC 1395w-113(a)(7) calls it an "income-related increase in the base beneficiary premium." It is 20 CFR 418.1101, Social Security's own regulation, that is headed "What is the income-related monthly adjustment amount?" The acronym is what almost everyone searches for, so that is what this page is titled, but the regulation is where the name comes from. Its purpose, stated in 20 CFR 418.1005(a), is to "reduce the Federal subsidy of the Medicare Part B program for beneficiaries with modified adjusted gross income above an established threshold," since premiums normally cover about 25 percent of Part B program cost and the government covers the rest.

Four features make IRMAA behave unlike almost anything else in the tax and benefits system, and each one catches people out for a different reason.

It runs on a two-year lag. Under 42 USC 1395r(i)(4)(B)(i), the income used is that "determined for the individual's last taxable year beginning in the second calendar year preceding the year involved." So a 2026 premium is set from a 2024 return. There is a fallback in clause (ii): if by October 15 before the year the Treasury lacks adequate electronic data for that year, the previous taxable year is used instead, with proper adjustments once the right data arrives. The consequence people feel is that a surcharge arrives exactly when income has fallen, typically in the first two years of retirement, and then disappears on its own without anyone doing anything.

It is a cliff, not a rate. The statute sets applicable percentages of program cost rather than dollar add-ons. A beneficiary below the threshold pays a premium covering roughly 25 percent of program cost; above it, the tiers charge 35, 50, 65, 80, and 85 percent. Crossing a threshold by one dollar moves the whole year into the next tier. Nothing about the surcharge is prorated against how far above the line the income sat, which is why the planning question is always the threshold and never the marginal rate.

The income measure is specific to this program. 42 USC 1395r(i)(4)(A) defines modified adjusted gross income as adjusted gross income under section 62 of the Internal Revenue Code, determined without regard to sections 135, 911, 931, and 933, and increased by tax-exempt interest received or accrued during the year. Note what it does not add back: nontaxable Social Security benefits. This is not the same MAGI used for the premium tax credit, and it is a different measure again from provisional income, which decides how much of a Social Security benefit is taxable and looks at the current year rather than at a return filed two years ago. Treating the three as one number is a reliable way to reach a wrong answer.

Filing separately is penalized by design. Ordinarily the joint thresholds are twice the single ones, with one exception written into 1395r(i)(3)(C)(ii): in the top row the joint figures are 150 percent of the single figures rather than double. And under (C)(iii), a person who is married at year end, does not file a joint return, and does not live apart from their spouse at all times during the year has each dollar amount in the ladder reduced by the single threshold amount for that year. The practical effect is that the surcharge begins at a far lower income for that filer than for anyone else. Living apart from the spouse for the entire year avoids the reduction, which is a narrow test and turns on the whole year.

The appeal exists but the door is narrow, and this is the fact most worth knowing in advance. 20 CFR 418.1205 lists seven major life-changing events: the death of a spouse; marriage; divorce or annulment; you or your spouse stopping work or reducing hours; loss of income-producing property, provided the loss was not at your direction and is not the result of ordinary investment risk; a scheduled cessation, termination, or reorganization of an employer's pension plan; and a settlement from an employer because of the employer's closure, bankruptcy, or reorganization. Section 418.1210 then closes the list in terms: "We will not consider events other than those described in § 418.1205 to be major life-changing events," specifically excluding events that affect expenses but not income, and losses of dividend income from ordinary investment risk. So a Roth conversion, a capital gain, an exercised option, or a large one-time withdrawal opens no appeal. The reason is not that income failed to fall afterwards, since it usually does. The reason is that the event is not on the list. The reduction also has to be significant in the regulation's sense under 418.1215, meaning it must actually move you to a lower tier or below the threshold. The form is SSA-44.

Part D works differently in three ways. Its surcharge is computed from a base beneficiary premium representing 25.5 percent of the cost of basic drug coverage. It reaches people in Medicare Advantage prescription drug plans, PACE, and cost plans as well as standalone Part D plans. And under 20 CFR 418.2125(b), you pay the Part D adjustment separately from your plan premium, regardless of how you pay the plan, which is why the surcharge shows up as a deduction from a Social Security payment rather than on the insurer's bill.

One genuinely fixed figure sits in the statute. The top tier begins at $500,000 for a single filer, and 42 USC 1395r(i)(5)(C) excludes that particular amount from the annual inflation adjustment that applies to every other threshold. It begins increasing in calendar years beginning after 2027, measured against an August 2026 price index. Every other threshold moves each year: CMS raises them by the change in the consumer price index, rounds to the nearest $1,000, and under 20 CFR 418.1105(c) publishes them in the Federal Register each September for the following year.

1. Social Security receives your income data from the IRS for the tax year two years back and compares your modified adjusted gross income against that year's published thresholds. Under 20 CFR 418.1005(b) and (c), CMS sets the standard premium and the late-enrollment rules while Social Security makes the income determination, which is why the appeal goes to Social Security.

2. You receive an initial determination notice, normally in the autumn, stating the tier and the amount for the coming year.

3. The Part B adjustment is added to your Part B premium, usually withheld from a Social Security payment. The Part D adjustment is billed separately from your drug plan premium and is not paid to the plan.

4. If a listed life-changing event has reduced your income, file Form SSA-44 with evidence of the event and of the more recent year's income. Social Security can then use the more recent year instead.

5. Otherwise it resolves itself. Because the measure is a return from two years earlier, a one-off spike stops mattering two years later without any action.

A hypothetical pair, which is the clearest way to see the closed list. Ines retires in June 2026. Her 2026 premiums were set from her 2024 return, when she was still working full time. Stopping work is item (d) on the list at 20 CFR 418.1205, so she files an SSA-44, documents the work stoppage, and asks Social Security to use her 2026 income instead. If the reduction is significant in the sense of 418.1215, the surcharge comes off. Marcus, in the same year, converted $180,000 from a traditional IRA to a Roth in 2024. His 2026 premiums reflect that income too. His 2025 and 2026 income are back to normal, but a conversion appears nowhere on the list, so no appeal is available to him. He pays the surcharge for 2026 and it ends by itself in 2027, when the 2025 return (2027 minus 2) becomes the measuring year. The difference between the two is not whether income fell. It fell for both. The difference is that one cause is on the list and the other is not, which is why IRMAA is a decision to make before the income year rather than a problem to fix afterwards.

Pros

• The tiers and thresholds are published in advance, so the cost of crossing a line is knowable before the income year rather than after it.
• The two-year lag cuts both ways: a temporary surcharge ends automatically, with no form to file and nothing to reclaim.
• There is a real appeal route with defined evidence requirements, and retirement itself is one of the qualifying events.
• The design is progressive in intent, charging higher-income beneficiaries a larger share of what the program actually costs.

Cons

• The cliff structure means a dollar of extra income can cost a full tier for twelve months, on both Part B and Part D.
• The two-year lag hits people whose income has already dropped, which is exactly when the bill is hardest to absorb.
• The list of appealable events is closed, so the most common causes of a one-off income spike are not appealable at all.
• Married filing separately while living with a spouse is treated far more harshly than any other status.
• The income measure differs from other MAGI definitions in the tax code, so a figure calculated for one purpose cannot be reused for this one.