Crossing the $109,000 IRMAA Line by One Dollar Costs $1,148.40 in 2026

A notice mailed in late 2025 told a group of Medicare enrollees that their 2026 Part B premium would not be $202.90 a month. It would be $284.10, or $405.80, or something higher. The income that produced that letter was earned in 2024, reported on a return filed in 2025, and cannot now be changed by anything the recipient does.

The income-related monthly adjustment amount, abbreviated IRMAA, is usually described as a surcharge on high earners. That description is accurate and close to useless, because it omits the two features that decide who pays and how much. The amount is set by a tax year two years in the past, and it moves in steps rather than in proportion. One additional dollar of modified adjusted gross income can add more than a thousand dollars to a year of premiums, and the notice that announces it does not show that arithmetic.

Two Tax Years Stand Between the Income and the Bill

The Social Security Administration states the input plainly: "To determine your 2026 income-related monthly adjustment amounts, we use your most recent federal tax return the IRS provides to us." In practice that is the return for tax year 2024, filed during 2025. The agency's Program Operations Manual System describes the same figure as MAGI "based on tax return two years prior, or three years if two years prior is unavailable," and cites 20 CFR 418.1115 for the Part B adjustment and 20 CFR 418.2115 for the Part D adjustment.

Three consequences follow from that two-year gap, and each one is easy to miss while reading a single year's notice.

• A change in circumstances shows up late. A person who stopped working in 2025 is still being billed in 2026 against 2024 wages. Absent an intervention described further down, the lower income does not reach the premium until the 2027 determination.
• The tax year that sets the 2028 premium closes on December 31, 2026. Anything that raises MAGI during the current calendar year is priced two years later, against thresholds that have not been published yet.
• A missing return moves the lookback back one more year. Where the two-year-prior return is not available to the agency, the three-year-prior return is used instead. POMS HI 01120.055 places the correction on the beneficiary rather than the agency: a person whose determination was built on three-year-old data "can request a new initial determination" once the two-year-old return exists. It is a request, not an automatic adjustment.

Source: Social Security Administration, Benefits Planner: Medicare Premiums, and SSA Program Operations Manual System HI 01101.020, citing 20 CFR 418.1115 and 20 CFR 418.2115.

A Cliff, Not a Phase-In

Federal income tax brackets are marginal. Crossing into a higher bracket changes the rate on the dollars above the line and leaves every dollar below it alone. IRMAA does not work that way. The threshold is a switch. Once MAGI passes it by any amount, the full adjustment for that band applies to all twelve months.

For premium year 2026 the Centers for Medicare & Medicaid Services published the following schedule for a single filer with full Part B coverage. The MAGI being measured is from tax year 2024.

• $109,000 or less — Part B premium $202.90, no Part D adjustment
• Over $109,000 up to $137,000 — Part B adjustment $81.20, total premium $284.10; Part D adjustment $14.50
• Over $137,000 up to $171,000 — Part B adjustment $202.90, total premium $405.80; Part D adjustment $37.50
• Over $171,000 up to $205,000 — Part B adjustment $324.60, total premium $527.50; Part D adjustment $60.40
• Over $205,000 and under $500,000 — Part B adjustment $446.30, total premium $649.20; Part D adjustment $83.30
• $500,000 or more — Part B adjustment $487.00, total premium $689.90; Part D adjustment $91.00

For a married couple filing jointly, CMS doubles the first four income boundaries — $218,000, $274,000, $342,000, and $410,000 — but not the last. The top band opens at $750,000 on a joint return, one and a half times the $500,000 single-filer figure rather than twice it. The dollar adjustments themselves are identical, and CMS states that the Part D figure is paid "in addition to their Part D premium," meaning the plan premium a member already pays to an insurer.

Adding the Part B and Part D adjustments together and multiplying by twelve produces the figure that matters to a household budget. CMS does not print this column.

For a single filer the annual combined adjustment runs $1,148.40, $2,884.80, $4,620.00, $6,355.20, and $6,936.00 across the five surcharged bands. The step from each band to the next is $1,148.40, then $1,736.40, then $1,735.20, then $1,735.20, then $580.80. The three middle steps are within a dollar and change of each other, which means the cost of crossing a line barely varies across the interior of the schedule. A household at $170,000 and a household at $410,000 face almost the same penalty for one dollar of carelessness.

Source: Centers for Medicare & Medicaid Services, fact sheet "2026 Medicare Parts A & B Premiums and Deductibles," November 2025. Annual totals calculated from the published monthly figures.

The Dollar That Crosses, and the Income That Undoes It

A single filer with 2024 MAGI of exactly $109,000 pays no adjustment in 2026. The same filer at $109,001 pays $1,148.40 across the year. The extra dollar of income is charged at roughly a hundred thousand percent, which is a way of saying the concept of a marginal rate does not describe what is happening.

The useful question is different: how much additional income is required before the household is not worse off. Ignoring income tax entirely, MAGI has to exceed $109,000 by more than $1,148.40, so the break-even sits at $110,148.40. Income tax makes it worse, because the surcharge is paid from money that has already been taxed. At an assumed 24 percent federal marginal rate and no state income tax, only 76 cents of each extra dollar survives, so the excess income must reach $1,511.05 — a MAGI of roughly $110,511 — before the crossing stops costing money.

The band between $109,001 and about $110,511 is therefore a stretch of income where earning more leaves the household with less. The second threshold produces a wider one. Crossing $137,000 adds $1,736.40 to the year, so under the same 24 percent assumption the excess must reach $2,284.74 before it pays for itself.

Married Filers Meet the Same Line Twice

The adjustment is charged per enrollee, not per return. When both spouses are enrolled in Part B and Part D, one crossing of a joint threshold is billed twice.

• Crossing $218,000 costs the couple $2,296.80 for the year
• Crossing $274,000 costs an additional $3,472.80
• Crossing $342,000 and again at $410,000 each cost an additional $3,470.40
• Crossing $750,000 costs an additional $1,161.60
• A couple in the top band pays $13,872.00 in adjustments across 2026, on top of two standard premiums

Filing separately does not soften this. CMS publishes a separate table for beneficiaries "who are married and lived with their spouse at any time during the taxable year, but file a separate return," and it collapses to three rows. Above $109,000 and under $391,000, the Part B adjustment is $446.30 and the Part D adjustment is $83.30. That is $6,355.20 a year. The first dollar over $109,000 on a separate return lands on the fourth-level surcharge rather than the first: $6,355.20 for the year against $1,148.40, five and a half times the step a single filer meets at the same number.

The Surcharge Rises Even When the Income Does Not

The five surcharged totals are not independent dollar amounts. Divide each 2026 Part B total by the standard $202.90 and the results are 1.4, 2.0, 2.6, 3.2, and 3.4. Run the same division on the 2025 figures, where the standard premium was $185.00 and the totals were $259.00, $370.00, $480.90, $591.90, and $628.90, and the same five multiples appear.

In both years the surcharged totals tracked the standard premium rather than moving on their own. When the standard premium rose 9.68 percent from $185.00 to $202.90, the top total rose 9.70 percent from $628.90 to $689.90, with no separate announcement about surcharges. Two years is not a rule, and CMS does not publish the multiples as such, but the pattern is what the published figures show.

Follow one household through that. A couple whose MAGI was identical in tax year 2023 and tax year 2024, both above the top boundary, paid $12,712.80 in combined adjustments during 2025 and pays $13,872.00 during 2026. Their income did not move. The bill rose $1,159.20.

Eight Events Reopen a Determination. A Roth Conversion Is Not One.

The Social Security Administration will use a more recent tax year than the standard lookback, but only after a qualifying event. POMS HI 01120.005 lists eight: death of a spouse, marriage, divorce or annulment, work reduction, work stoppage, loss of income-producing property, loss of an employer pension, and receipt of a settlement payment from a current or former employer. The same section states that "our list of LCEs for IRMAA purposes is exclusive."

The exclusion list is where most planning errors land. POMS identifies ordinary loss of dividend income, higher medical expenses, higher living expenses, loss of child support, and loss of alimony as events that do not qualify, along with a voluntary sale of income-producing property. It also classifies one-time income increases — capital gains, lottery or casino winnings, IRA conversions, and cashing bonds — as non-qualifying events.

That last item deserves its own sentence. A Roth conversion that pushes MAGI across a threshold is not appealable on the ground that it was a one-time event. The surcharge it triggers is charged for the full premium year and then falls away when the lookback moves past it.

Where an event does qualify, the form is SSA-44, and POMS HI 01120.030 describes the evidence accepted for a work stoppage: a statement from an employer, a retirement letter, corporate minutes, a record of a business transfer or sale, or the beneficiary's attestation under penalty of perjury. The same section limits the scope: "All LCE reports only apply to the reporting spouse." Where an event does not qualify but the underlying figure is wrong, SSA separates two paths. For an amended return it asks only that the beneficiary "let us know" that the MAGI it counted has changed, and it states that "you don't need to file an appeal if you've shown us the information we used is wrong." The Request for Reconsideration, SSA-561-U2, is the instrument for disagreeing with the determination itself, not for correcting the data behind it.

The Threshold and the Premium Have Not Moved Together

The first threshold and the standard premium are both reset each November, from different mechanics. Reading the CMS fact sheets in sequence shows how far apart they have drifted. In 2019 the first single-filer threshold was $85,000 and the standard premium was $135.50. The pairs since: $87,000 and $144.60 in 2020, $88,000 and $148.50 in 2021, $91,000 and $170.10 in 2022, $97,000 and $164.90 in 2023, $103,000 and $174.70 in 2024, $106,000 and $185.00 in 2025, and $109,000 and $202.90 in 2026.

Source: Centers for Medicare & Medicaid Services, annual "Medicare Parts A & B Premiums and Deductibles" fact sheets, 2019 through 2026. Index calculated from the published figures.

Over those seven years the threshold rose 28.2 percent, a compound rate of about 3.62 percent a year. The standard premium rose 49.7 percent, about 5.94 percent a year. The premium moved at roughly 1.6 times the pace of the line that exempts a household from paying a multiple of it. One year runs the other way: the standard premium fell from $170.10 in 2022 to $164.90 in 2023, the only decline in the series.

The top boundary has not moved at all. Every CMS fact sheet from 2019 through 2026 places it at $500,000 for a single filer and $750,000 for a joint return, while each of the four lower boundaries moved every year. The band immediately below the top has therefore been compressed from below while its ceiling stayed fixed: in 2019 it ran from $160,000 to $500,000, a width of $340,000, and in 2026 it runs from $205,000 to $500,000, a width of $295,000. It has narrowed in every one of the seven years.

Numbers to Re-check

Every figure above carries a year, and most of them are replaced each November when CMS publishes the following year's fact sheet.

• Standard Part B premium, $202.90 a month — premium year 2026. Source: CMS annual premiums and deductibles fact sheet. Replaced each November.
• First threshold, $109,000 single and $218,000 joint — premium year 2026, measured against tax year 2024 MAGI. Same fact sheet, same November cycle.
• Part B annual deductible, $283 — premium year 2026, up from $257 in 2025. Not income-adjusted, and unaffected by everything above.
• Part D adjustments, $14.50 through $91.00 — premium year 2026. Same fact sheet.
• Top boundary, $500,000 and $750,000 — unchanged in every fact sheet from 2019 through 2026. Confirm before assuming it holds for 2027.
• The eight life-changing events — POMS HI 01120.005. Check the revision date printed at the top of the section, since POMS is amended without notice.
• Form numbers SSA-44 and SSA-561-U2 — confirm the current edition on the SSA forms index before filing.

Where This Doesn't Apply

The arithmetic above is the general schedule. Several conditions take a household outside it.

• MAGI at or below the first threshold. There is no adjustment, no step, and no reason to model any of this. The great majority of enrollees sit here.
• No Part B or Part D enrollment. The adjustment is an addition to a premium. A person who has deferred Part B while covered by active employment has no premium for it to attach to.
• The break-even figures rest on one assumption. The 24 percent marginal rate used above is illustrative. State income tax, the share of Social Security benefits pulled into taxable income by the extra dollars, and the net investment income tax all move the break-even, in most cases upward.
• A life-changing event resets the input. Where one of the eight events applies, the comparison is no longer between two tax years but between a tax year and an estimate the agency accepts, and none of the lookback arithmetic here describes it.
• A reported event covers only the spouse who reports it. POMS HI 01120.030 is explicit on this point, so a couple cannot assume one filing covers both determinations.
• Anything priced against 2026 income is being priced against unpublished numbers. The 2028 thresholds do not exist yet. A conversion sized to stay under a boundary this year is being sized against a boundary that will move.

This article explains how the rules are written. It is not tax, legal, or insurance advice, and it does not account for any individual situation. Amounts and thresholds change; verify the current figures at the source listed above before acting.