One dollar over, and the whole premium steps up.

The facts, in one place.

Six quotable sentences from the CMS 2026 tables. Quote them with the year attached.

1. The 2026 Medicare premium is set by income from the 2024 tax return, two years back. The standard Part B premium is $202.90 a month; the income-related surcharges begin above $109,000 of modified adjusted gross income on an individual return and $218,000 on a joint return.
2. One dollar over a threshold moves the whole premium up a step. At $109,001 of 2024 income, a single filer pays $284.10 for Part B plus a $14.50 Part D surcharge: $1,148.40 more for the year than a neighbor one dollar under.
3. There are six tiers. The first surcharge adds $81.20 a month to Part B and $14.50 to Part D; the top tier, at $500,000 and above on an individual return, adds $487.00 and $91.00, for a Part B premium of $689.90.
4. A married couple filing jointly at $750,000 of income pays $1,379.80 a month for two Part B premiums, before Part D.
5. The surcharge is not a marginal tax. It applies to the whole premium, so the cost of crossing a threshold is the same whether you cross it by one dollar or by ten thousand.
6. If income has dropped since the 2024 return because of retirement, a death, a divorce, or another listed life-changing event, Social Security will use the more recent year on request (Form SSA-44).

The tiers.

Every tier, exactly as CMS publishes it, with the yearly cost of each step worked out. Married filing separately: $109,000 or less pays the standard premium; over that and under $391,000 pays the fifth row; $391,000 and above pays the sixth. Source: CMS.

How IRMAA works.

Two years back. Medicare cannot see this year's income, so it uses the last return the IRS has finished with: for 2026 premiums, the 2024 return. The number it reads is modified adjusted gross income, which is adjusted gross income plus tax-exempt interest. A Roth conversion, a large capital gain, or a business sale in one year shows up as a higher premium two years later, and then goes away again.

A staircase, not a slope. The surcharge is a fixed amount per tier, not a percentage of income over the line. Crossing a threshold by one dollar costs the same as crossing it by ten thousand: the whole step, twelve months, per person on Medicare. That is why the calculator shows the room to the next threshold.

Part B and Part D both. The Part B surcharge is added to the standard premium of $202.90. The Part D surcharge is separate, paid to Medicare rather than to the drug plan, on top of whatever the plan charges. A couple on Medicare pays each surcharge twice.

When the income is out of date. If income has dropped since the return Medicare used because of retirement or reduced work, a marriage, divorce, or the death of a spouse, the loss of a pension, or an employer settlement, Social Security will recalculate on a more recent year. The form is SSA-44, and it can be filed the same year the premium notice arrives.

What this page does not do. It does not compute modified adjusted gross income; enter it from the return. It does not model the Part D plan premium, the late-enrollment penalties, or the hold-harmless rule for Part B increases. It shows the tier and what the tier costs. Educational, not advice.

Worked examples.

Official rows walk the CMS table's own boundaries, one dollar either side, and the engine must place each in the tier the table states. Derived rows are ours from the same table.

The staircase, drawn.

Monthly Part B premium plus the Part D surcharge for an individual return, against 2024 income. Free to reuse with its attribution; there is a download below.

Methodology.

Premium year 2026; income year 2024; record reviewed September 4, 2026.

1. Input. Modified adjusted gross income from the return two years before the premium year, and the filing status on that return.
2. Tier. The CMS table applied literally: tiers one through four are “over the previous bound and not over this one,” the fifth is “under $500,000” on an individual return, and the sixth begins at $500,000. Joint returns use the joint column; married filing separately uses its own three-step rule.
3. Amounts. The Part B adjustment and total, and the Part D adjustment, as the table states them. The yearly cost is the two monthly adjustments times twelve.
4. Room to the next tier. The next tier's first dollar minus the entered income minus one: how much more income would still have stayed in the current tier.
5. Validation. Each Part B total must equal the standard premium plus the row's adjustment; adjustments and bounds must ascend; the joint bounds must be double the single bounds for the first four rows; and every boundary case above must land in its stated tier.
6. Not modeled. The computation of MAGI itself, the Part D plan premium, late-enrollment penalties, hold-harmless, and any change after the review date.

Sources.

1. 1. Centers for Medicare & Medicaid Services, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet, November 14, 2025). The Part B standard premium and deductible, the Part A inpatient deductible, and every row of the Part B and Part D income-related adjustment tables. Retrieved September 4, 2026; verified September 4, 2026.
2. 2. United States Code (Cornell LII), 42 U.S.C. § 1395r(i) — Income-related increase in Part B premium (and, by cross-reference, Part D). That the income used is modified adjusted gross income from the return two years before the premium year, and the mechanism of the tiers. Retrieved September 4, 2026; verified September 4, 2026.

Every other 2026 figure, with its release, is on the retirement numbers page.

Revision history.

September 4, 2026

First release of the annual numbers record and page for 2026, and of the IRMAA tool built on its Medicare section: plan and IRA limits from Notice 2025-67, HSA figures from Rev. Proc. 2025-19, Social Security figures from the Federal Register notice, Medicare premiums and both income-related tables from the CMS fact sheet, the standard deduction and gift exclusion from Rev. Proc. 2025-32, and the senior deduction from the IRS's OBBBA guidance.

Canonical address: https://consideratecapital.com/tools/irmaa-calculator