A tax return you filed two years ago is setting this year's premium.

Part 1

The bill arrives two years late

Most people meet this rule by opening a letter. The premium is going up, by an amount nobody quoted, for a reason that is not explained in the letter in any way that helps.

The reason is a federal surcharge with an unmemorable name: the income-related monthly adjustment amount. It is added on top of the standard Medicare Part B premium, and separately on top of whatever a Part D drug plan charges. The agency puts it at roughly eight percent of people with Medicare Part B, and roughly eight percent of those with Part D.

Two features make it behave unlike almost anything else in a household budget. It is normally calculated from a tax return filed two years earlier, so the income that triggers it belongs to a year that is closed, filed and spent. And it does not phase in. Income is sorted into bands, and crossing from one band into the next by a single dollar moves the whole premium to the higher figure for twelve months.

Where the tax authority has not yet supplied that two year old figure, the agency uses the three year old one instead until it can. And where no return was filed at all for a year in which income was above the threshold, federal rules direct the agency to impose the highest adjustment for that filing status until the position is corrected. Not filing is the most expensive option available.

These are federal rules, applied identically in every state. State income tax treatment of the same money varies, but the Medicare surcharge itself does not.

This guide is educational information. It is not legal, tax or financial advice.

Part 2

What the surcharge actually costs

The surcharge is set from modified adjusted gross income, sorted into six bands. The first band is where the surcharge is zero. Both Part B and Part D carry their own surcharge at each step, and both are charged per person, so a couple who are both on Medicare each pay it.

Every figure above is a monthly amount for 2026, and every one is on top of what would otherwise be paid. The standard Part B premium in 2026 is $202.90 a month, so someone in the top band pays $689.90 for Part B alone, plus $91.00 added to their drug plan.

Read down the Part B column and the shape of the thing becomes clear. The steps are not gentle. The second band adds $81.20 a month. The third more than doubles that. At the top, the surcharge on Part B alone is more than twice the standard premium.

Part 3

One dollar, and a year of it

Income tax works in marginal bands. Earning a dollar above a bracket line taxes that dollar at the higher rate, and only that dollar. Almost everyone assumes the Medicare surcharge behaves the same way. It does not.

The surcharge is a cliff. A single person with modified adjusted gross income of $109,000 in the relevant tax year pays no surcharge at all. A single person with $109,001 pays $81.20 a month on Part B and $14.50 a month on Part D. That is $95.70 a month, and it runs for twelve months, so one dollar of income costs $1,148.40.

The same shape repeats at every line. It is at its most brutal at the top: a single person at $499,999 pays $446.30 and $83.30, and one at $500,000 pays $487.00 and $91.00. Across the whole range, someone in the top band pays $578.00 a month more than someone in the bottom band, which is $6,936.00 across the year, for each person on Medicare.

Part 4

What the figure is actually made of

The figure the surcharge reads is modified adjusted gross income, and the modification matters. It is adjusted gross income with tax-exempt interest added back.

That single addition surprises people. Municipal bond interest is exempt from federal income tax and is counted in full here. Money arranged specifically to be tax-free still moves a household toward a bracket line, and can push it over one.

The things that most often push a return into a higher band are one-off rather than recurring:

• The sale of a property, where the gain above any available exclusion lands in a single year.
• A Roth conversion, which is deliberately taxable income by design.
• A large withdrawal from a retirement account, including a first required minimum distribution.
• The final full year of work before retiring, which is often the highest-income year of a life and sits exactly two years before the first premium is set.
• The year a spouse dies, where a couple's joint income can be assessed against the joint thresholds while the survivor is later assessed alone.

Because the surcharge is set per person, a couple both enrolled in Medicare pay it twice. Two people in the second band pay $95.70 each, which is $191.40 a month for the household.

The reverse case surprises people more. The bands are read against the return, so a couple who filed jointly are measured against the joint figure and the joint thresholds even when only one of them is enrolled in Medicare. A spouse who is younger, still working and not yet on Medicare does not shelter the enrolled one; their income is in the same number.

Part 5

The seven events that let you argue

Federal regulation allows the agency to use a more recent tax year, rather than the one from two years ago, when a major life-changing event has significantly reduced income. The list of events that count is closed, and it contains seven:

• Your spouse dies.
• You marry.
• Your marriage ends through divorce or annulment.
• You or your spouse stop working, or reduce the hours you work.
• You or your spouse lose income-producing property, provided the loss was not at your direction and not the ordinary risk of investment. The regulation names disaster, disease, arson, and fraud or theft by a third party as examples.
• You or your spouse experience a scheduled cessation, termination or reorganization of an employer's pension plan.
• You or your spouse receive a settlement from an employer or former employer because of that employer's closure, bankruptcy or reorganization.

The fourth is the one that applies most often, because retiring is a work stoppage and retiring is precisely what happens between the trigger year and the year the premium is charged. Reducing hours counts too, which is easy to overlook.

The request is made on a form, with evidence of the event and an estimate of the more recent year's income. It can be filed as soon as the letter arrives, and there is no need to wait for the tax year to end.

What it does not do is settle the matter permanently. A granted request covers the year you asked the agency to use and the following year where that applies, so an income that stays low may need the request making again rather than carrying forward on its own.

Two further routes exist that have nothing to do with life events, and they are covered in Part 8: correcting the figure where a return was later amended, and challenging it where the agency worked from income information that was wrong. Those are arguments about the number rather than about a change in circumstances.

Part 6

What is not on the list

The list in the previous part is closed, and the exclusions follow from it directly. None of the following is a major life-changing event, however unrepeatable it was:

• A Roth conversion.
• Selling a house, a business or an investment property at a gain.
• A one-off large withdrawal from a retirement account.
• A required minimum distribution beginning.
• An inheritance received.
• A capital gain distribution from a fund.

There is a hard logic to it. The listed events are things that happen to a person and reduce their income. The unlisted ones are transactions that raise income, generally chosen, and often chosen for good reasons. The surcharge treats a deliberate one-year spike as exactly what it is, and charges for it two years later.

Part 7

The filing status that costs the most

Filing separately while married carries its own set of thresholds, and they are severe in a way the main table does not show.

A married person who lived with their spouse at any time during the year and files a separate return gets three bands rather than six. Below $109,000 there is no surcharge. Above $109,000 and below $391,000, the Part B surcharge is $446.30, which is the fifth of the six figures in the main table. At $391,000 and above it is $487.00, the top figure.

Set that beside a single filer. At a modified adjusted gross income of $115,000, someone filing as a single person pays $81.20 a month on Part B. Someone married, filing separately and having lived with their spouse at any point that year, pays $446.30. The income is identical. The surcharge is more than five times larger.

There is one route around it, and it is narrow. The ordinary single-filer bands apply to a married person filing separately only where they lived apart from their spouse for the entire tax year. The year that matters is the one the figure comes from, two years back, not the year the premium is being charged. Any part of that year living together puts them in the three-band table.

Part 8

How it reaches you, and the bill people miss

The Social Security Administration decides who pays these surcharges and how much, for Part B and for Part D alike. That is worth knowing on its own, because it means the drug plan did not set the Part D figure and cannot change it.

The Part B surcharge is straightforward. It is added to the Part B premium and comes out of the Social Security payment before it arrives, which is why the first sign of it is usually a smaller deposit.

The Part D surcharge behaves differently, and this is where people get caught. It is paid on top of whatever the drug plan charges, and it does not go to the plan. Someone who pays their plan premium directly, by card or by bank transfer, keeps doing exactly that, and then receives a separate government bill for the surcharge. It looks like a mistake. It is not, and ignoring it puts drug coverage at risk.

Disagreeing with the figure

Two different arguments are available and they are not the same thing. One is that a listed life event has reduced income, which is the request covered in Part 5. The other is that the income figure itself is wrong. Where a return was amended after it was filed, there is a separate rule allowing the amended figure to be used, and it has to be raised rather than assumed.

Part 9

The one afternoon checklist

The first three establish whether a surcharge is being charged and on what basis. The rest decide whether anything can be done about it.

• Find the letter and read which tax year it names. It will be two years before the premium year, and it is the only year that matters.
• Pull that year's tax return and find adjusted gross income, then add any tax-exempt interest. That sum is the figure being used.
• Compare it against the bands. Note how far above a line it fell, because a small distance is worth knowing about for future years.
• List anything that has happened since that year: retirement, reduced hours, a death, a marriage, a divorce, a pension ending, an employer settlement. If any of the seven applies, request a new determination.
• File the request as soon as the letter arrives, with evidence of the event and an estimate of the more recent year's income. Do not wait for the year to end.
• If nothing on the list applies, check the figure itself for accuracy. The surcharge rests on what the tax authority reported, and a corrected or amended return is a separate ground for asking the agency to look again.
• If a drug plan is paid directly rather than deducted, watch for a separate government bill for the Part D surcharge and pay it. It does not go to the plan.
• If married and filing separately, check what the joint thresholds would have produced against the three separate bands. The gap can be several thousand dollars a year.
• Before any large one-off transaction, work out where the resulting income lands against the bands, and by how much it crosses a line. The surcharge is not appealable on those grounds afterwards.