The simple version

Most people in the program pay one standard monthly figure. Above a certain income an extra amount gets added, and it applies to both of the parts that carry a monthly charge.

The income used is not this year's. The rules point the agency at the return filed two years before the year being billed, and at the one from three years before when the newer one has not arrived yet.

The income lines are also edges rather than ramps. Going one dollar past one of them moves the whole extra amount to the next level, not by a sliver.

The numbers

• The Medicare Open Enrollment Period runs from October 15 to December 7 (Centers for Medicare and Medicaid Services, Medicare.gov, joining a plan, read October 15, 2026)
• The rules direct the agency to use the modified adjusted gross income provided by the IRS for the tax year 2 years prior to the effective year, and the year 3 years prior when the IRS has not provided the newer figure, adjusting later (20 CFR 418.1135(a) and (b), applied to prescription coverage by 20 CFR 418.2135)
• For calendar years 2011 through 2019 the income threshold was $85,000 for single filers and $170,000 for joint filers (20 CFR 418.1105(b) for Part B, and 418.2105(b) for prescription coverage)
• For calendar years beginning in 2019 the single-filer ranges were set with lines at $85,000, $107,000, $133,500, $160,000 and $500,000 (20 CFR 418.1115(b)(3))
• Beginning after 2019 CMS sets the income ranges by increasing the preceding year's by any percentage increase in the Consumer Price Index, rounded to the nearest $1,000, and publishes them in September each year (20 CFR 418.1115(e)(1), with the same text at 418.2115(e)(1) for prescription coverage)
• The $415,000, $500,000 and $750,000 amounts in those ranges are not adjusted that way until 2028, with CMS adjusting them beginning in 2027 for the following year; the $415,000 line applies to married people who file separately and lived with their spouse during the year (20 CFR 418.1115(d) and (e)(2), with the same text at 418.2115(e)(2))
• For 2026 the standard Part B monthly figure is $202.90 (Medicare Program; Medicare Part B Monthly Actuarial Rates, Premium Rates, and Annual Deductible Beginning January 1, 2026, 90 FR 52063, document 2025-20251, published November 19, 2025)
• The 2026 Part B steps for single filers run: at or below $109,000, nothing added, $202.90 total; above $109,000 to $137,000, $81.20 added, $284.10 total; above $137,000 to $171,000, $202.90 added, $405.80 total; above $171,000 to $205,000, $324.60 added, $527.50 total; above $205,000 and below $500,000, $446.30 added, $649.20 total; at or above $500,000, $487.00 added, $689.90 total (same notice)
• The joint-filer figures for those same steps are $218,000, $274,000, $342,000, $410,000 and $750,000 (same notice)
• No notice setting the 2027 Part B monthly figure or the 2027 income-related amounts had been published in the Federal Register as of October 15, 2026. A search of the Federal Register for the exact title phrase used by the annual notice returns the November 19, 2025 document for 2026 and nothing published in 2026, and a broader phrase search across 2026 also returns nothing

Where the income figure comes from

The lookback is the part that catches people. A year in which someone sold a property or received an unusually large one-off sum sets the amount they are billed two years later.

By then the income is gone and the amount is not. A separate route exists for life-changing events, and this article does not cover what qualifies or what that route involves.

The second quirk is in how the lines themselves move. The rules index them to consumer price increases, rounded to the nearest thousand dollars, and publish the updated set each September.

The highest line for each filing status is the exception. The rules hold the 500,000 and 750,000 dollar edges, and a 415,000 dollar one for some married people filing separately, out of that indexing, so while the lower lines have climbed every year, those have stayed where they were set.

The actual math on 109,000 and 81.20

Take the first edge on the 2026 schedule for the larger of the two charges. A single filer at or below 109,000 dollars has nothing added. At one dollar more, 81.20 gets added every month.

That is 974.40 across a year for that one dollar, which is our multiplication of a published figure by twelve. Nothing phases in and nothing is prorated.

The third level is worth seeing too. The added amount there is 202.90, the same as the standard figure itself, so the monthly total of 405.80 is the base plus that much again.

Now the frozen edges. The lower lines have moved from 85,000 to 109,000 dollars for a single filer since 2019, a rise of about 28 percent by our arithmetic, while the 500,000 dollar line has not moved at all.

That squeezes the one underneath it. In 2019 the top level for a single filer opened at 160,000 and ran to 500,000, a width of 340,000 dollars.

In 2026 it opens at 205,000 and still ends at 500,000, a width of 295,000. Both widths are our arithmetic on published figures.

What this means

The window that opens today runs to December 7 and covers next year's coverage, and the amount higher earners will have added for that year is not published yet. The current published figures are the 2026 set, and last year's notice was published on November 19.

A forecast of those figures is not the same thing as the figures. Anything quoting 2027 amounts right now is projecting from the indexing formula rather than reading a notice, because as of today no such notice exists.

The structural point outlasts any one year. An edge that does not move while incomes and prices do will be crossed by more people over time without anyone's real position changing, and the rules themselves say when that pause is scheduled to end.

What this is NOT

This article explains how the income-related amount added to Medicare Part B and Part D is determined and how its income lines are set, using 20 CFR 418.1105, 418.1115, 418.1135, 418.2105, 418.2115 and 418.2135 as published in the annual Code of Federal Regulations, the Federal Register notice setting the 2026 Part B figures published November 19, 2025, and Medicare.gov, all read on October 15, 2026. It is not advice about enrolling in, keeping, dropping or switching any plan, and it is not a recommendation of any plan, insurer or coverage option. It is not tax advice and contains no strategy for lowering anyone's income, reported income, or the amount they are charged. It does not tell any reader what they will be billed: the arithmetic in the actual math section is ours, labelled as such, run on published figures, and an individual determination is made by the Social Security Administration from that person's own record. It states no 2027 figure, deliberately, because no notice setting those amounts had been published when this was written, and it makes no projection of what they will be. It does not cover the separate process for life-changing events, the low-income subsidy, or appeals, none of which it describes. The regulation text cited is the annual edition dated April 1, 2025, and later amendments may exist that this article does not cover. Medicare is a public program rather than an employee benefit, and nothing here describes any employer's plan. It is not a statement about whether these amounts or income lines are set at the right level. This is not a political endorsement or criticism of anyone.

Sources

• 20 CFR 418.1105, What is the threshold (Part B), annual edition dated April 1, 2025, read October 15, 2026
• 20 CFR 418.1115, What are the modified adjusted gross income ranges (Part B), annual edition dated April 1, 2025, read October 15, 2026
• 20 CFR 418.1135, What modified adjusted gross income information will we use, annual edition dated April 1, 2025, read October 15, 2026
• 20 CFR 418.2105, 418.2115 and 418.2135, the corresponding prescription coverage sections, annual edition dated April 1, 2025, read October 15, 2026
• Medicare Program; Medicare Part B Monthly Actuarial Rates, Premium Rates, and Annual Deductible Beginning January 1, 2026, 90 FR 52063, document 2025-20251, published November 19, 2025, read October 15, 2026
• Centers for Medicare and Medicaid Services, Medicare.gov, Joining a plan, read October 15, 2026