According to the Social Security Administration, Medicare’s income-related monthly adjustment amount (IRMAA) is calculated using the most recent federal tax return the IRS provides—often from two years earlier. That timing can surprise people who had a one-time income spike, then moved into a lower-income year. The result is a higher Medicare Part B premium and an added Part D surcharge that can show up long after the “big income year” is over. Understanding what triggers IRMAA, and what relief options exist, can help prevent an avoidable premium shock.

Quick takeaways

IRMAA is a Medicare surcharge tied to MAGI from a prior tax return, not current monthly income.
A one-year income spike (capital gains, Roth conversion, severance) can raise premiums two years later.
MAGI for IRMAA includes tax-exempt interest, a line item that catches some filers off guard.
If an amended return changes the income SSA used, the surcharge can be corrected with documentation.
If income dropped after specific life-changing events, SSA may reduce IRMAA using Form SSA-44.

The IRMAA “trap” starts with a tax return you already filed

IRMAA is not a penalty for signing up late or choosing the wrong plan. It is an income-based adjustment that applies to Medicare Part B and Part D when income is above certain thresholds.

The “trap” is the timing. SSA generally uses IRS data from a prior tax year to set the premium year’s IRMAA. For many beneficiaries, that means the tax return from two years earlier drives today’s premium decision.

That gap matters because retirement income is rarely smooth. A move, a sale, or a single big distribution can make one tax year look unusually high, even if income is lower now.

MAGI is the number that matters—and it is not just “taxable income”

For IRMAA, SSA looks at modified adjusted gross income (MAGI). In SSA’s guidance, MAGI generally equals adjusted gross income (AGI) plus tax-exempt interest.

That “plus tax-exempt interest” detail is where confusion starts. Interest from municipal bonds may be exempt from federal income tax, but it still counts toward MAGI for IRMAA calculations.

Another common misconception is that deductions or itemizing changes IRMAA directly. Deductions can affect taxable income, but IRMAA is built off MAGI as reported through the IRS data SSA receives.

Common one-year income spikes that trigger IRMAA later

Many IRMAA surprises come from income that is legitimate, planned, and temporary.

Examples that can lift MAGI for a single tax year include:

Realizing large capital gains from selling investments.
A Roth conversion that moves money from a traditional IRA to a Roth IRA.
Large IRA/401(k) distributions, including lump-sum withdrawals.
Severance, a bonus, or higher wages in the final working year.
A sale of business or rental property that produces gains.
A one-time settlement payment.

None of these events automatically mean “too much income.” The issue is that crossing a threshold can move a beneficiary into a higher IRMAA tier, and the premium impact arrives later—often when the event is no longer top of mind.

What the surcharge can look like in 2026

CMS sets the standard Part B premium each year, and IRMAA tiers add on top of that.

For 2026, CMS says the standard Part B premium is $202.90 per month. Higher-income tiers pay more, up to a $689.90 total monthly Part B premium at the top bracket.

Part D works differently: the IRMAA is a monthly surcharge added to whatever the plan premium is. For 2026, CMS lists Part D IRMAA amounts that range from $14.50 up to $91.00 per month, depending on income tier.

A practical way to think about the risk is “two checks.” First, a prior-year return determines whether IRMAA applies. Second, the premium year bill shows up automatically through Social Security withholding or direct billing.

When SSA used the “wrong” tax year: timing issues and amended returns

SSA notes that it generally uses the most recent return the IRS provides. In some cases, SSA may still be working off an older return if the newest one was not available in time.

If a newer return exists—or a return was not required—SSA guidance encourages beneficiaries to contact the agency so the record can be updated.

Amended returns are another overlooked fix. If an amendment changes the MAGI SSA used, SSA says it can update the determination if the beneficiary provides a copy of the amended return and IRS acknowledgment.

The official relief valve: life-changing events and Form SSA-44

There is a specific mechanism to ask SSA to use more recent income information: Medicare Income-Related Monthly Adjustment Amount—Life-Changing Event (Form SSA-44).

SSA’s form lists qualifying life-changing events, including:

Marriage
Divorce/annulment
Death of a spouse
Work stoppage or work reduction
Loss of income-producing property
Loss of pension income
Employer settlement payment

The key is that the request is tied to a life-changing event that reduced income, not simply a preference to pay less. Documentation matters, and SSA may request evidence that supports the updated income estimate.

What you can do before filing season—and before Medicare starts

IRMAA is often avoidable, but not with last-minute moves. The two-year lookback means today’s tax decisions can echo into future Medicare premiums.

Here is a practical checklist:

Identify any “one-time income” items likely to hit this year’s return (gains, conversions, lump-sum distributions).
Check whether tax-exempt interest will be unusually high.
If income will drop because of a qualifying life event, gather paperwork early and consider the SSA-44 pathway.
If a return will be amended, keep the IRS acknowledgment and a clean copy ready for SSA.
If Medicare enrollment is coming soon, map major income events across multiple years, not just the current year.

What this means in the United States

IRMAA rules are federal and apply nationwide to Medicare Part B and Part D. The key inputs—MAGI, filing status, and the prior-year return SSA receives from the IRS—work the same across states.

Where location can matter is the mix of income sources a household typically has (for example, interest-heavy portfolios or property-related income). But the determination process and appeal options are uniform because Medicare and SSA rules are national.

What to watch next

IRMAA thresholds and premium amounts can change each year. CMS publishes the annual Part B premium and related IRMAA tables, and SSA updates beneficiary guidance and forms as needed.

For beneficiaries near an income threshold, even routine year-end income events can change the next determination cycle. Monitoring MAGI in real time—especially in years with planned transactions—can reduce the odds of a “surprise premium” arriving two years later.

SOURCES

DISCLAIMER

General information only; not financial advice. Medicare and tax rules can change, and individual situations vary. Consider contacting Social Security for case-specific questions and a qualified tax professional for return- and income-planning implications.

Medicare IRMAA: The 2-Year Lookback That Can Raise Part B and Part D