An unexpected Medicare deduction can look like a billing mistake when you are comparing it with the advertised standard premium. Before deciding whether it is wrong, separate three questions: which premium year the notice covers, which tax return supplied the income, and which beneficiary is being charged. IRMAA connects those questions, but it does not turn them into one household insurance policy. This guide provides a way to investigate the number before changing an investment, filing a request or assuming your retirement budget was incorrect.
Start with the charge, not an age rule
IRMAA means income-related monthly adjustment amount. It adds an income-based amount to Medicare Part B and prescription drug coverage for affected beneficiaries. Part B has a published standard premium as well as its income surcharge. Part D has an income surcharge that is separate from whatever the drug plan itself charges. A person enrolled in both components can encounter both adjustments. A person with different coverage months needs those months considered separately.
This is why a statement such as “Medicare costs this much after age 65” is incomplete. Enrollment dates differ, and some people qualify before 65. The calculator asks about actual coverage rather than deciding eligibility from a birthday. It also does not model every part of a Medicare budget: deductibles, coinsurance, Medigap, many Medicare Advantage arrangements and medical spending are separate. Treat a premium estimate as one line in the budget, not a complete health-expense forecast.
Identify the published 2026 schedule
CMS published a standard monthly Part B premium of $202.90 for 2026. For the ordinary individual schedule, no income surcharge applies at MAGI of $109,000 or less. For married filing jointly, the corresponding first threshold is $218,000. The individual intermediate boundaries are $137,000, $171,000 and $205,000; the highest tier starts at $500,000. Joint intermediate boundaries are $274,000, $342,000 and $410,000, with the highest tier starting at $750,000.
Those figures describe the individual and joint schedules, not every possible filing situation. Married filing separately has a special accelerated schedule when the spouses lived together during the tax year. The lived-apart exception has an SSA procedure of its own. A single comparison with the joint threshold can therefore give a seriously misleading result if the return was actually separate. Read the filing classification on the return and the notice before interpreting the table.
Ordinary thresholds keep the exact published boundary in the lower band. The final boundary behaves differently: the highest tier begins exactly at its stated starting amount. The portal's reference table and calculator show those distinctions explicitly. The reason to keep cents visible is accuracy, not an invitation to assume that an uncertain year-end income estimate can be controlled to the penny.
Reconcile the income measure
For IRMAA, the starting measure is federal adjusted gross income plus tax-exempt interest. It is not taxable income after deductions, total cash received, gross investment sale proceeds or a MAGI definition used by another program. When the calculator asks for AGI, use the AGI associated with the relevant return or a carefully prepared estimate. Then supply the separate tax-exempt-interest figure. Adding income already included in AGI a second time overstates the result.
Consider an invented household reviewing a return that already includes taxable pension payments and a taxable IRA distribution. They should not enter the return's AGI and add those payments again. Conversely, leaving out the tax-exempt-interest add-back understates Medicare MAGI. A useful reconciliation page lists the return year, the AGI line, tax-exempt interest and their sum, with a note explaining whether the amounts are filed or estimated.
Connect the return and the beneficiary
The ordinary lookback for 2026 premiums is the 2024 tax return. If that information is unavailable, SSA may use older information within its rules. A recent reduction in income does not by itself make the old return disappear. Certain circumstances can support a new initial determination, and disagreement with a determination can involve a different review procedure. The appropriate route depends on the notice and facts; a calculator result cannot establish it.
Joint filers also need to remember that IRMAA is assessed per beneficiary. Two enrolled spouses can each owe a surcharge even though one joint return supplies the income. If only one spouse has Part D, only that person's Part D coverage belongs in the calculation. If a spouse starts Part B halfway through the year, an annual household sum should count the actual months rather than blindly doubling a twelve-month individual result.
Use an estimate as a decision aid
Work through the calculation in a consistent order: choose the premium year, verify the ordinary income year, identify filing status, reconcile MAGI, then enter each person's coverage. Keep an unknown drug-plan premium unknown. The absence of that premium does not prevent calculating the statutory surcharge, but it does prevent claiming to know the entire drug-coverage cost. The report labels that distinction so the known amount is not mistaken for a final bill.
A planning result is most useful when you can explain what would change it. Possible changes include a corrected return amount, another coverage month, different actual plan premiums or an SSA-approved adjustment. The published 2026 schedule is a historical fact; a future premium schedule is not supplied by reusing it. Save the assumptions with any printed estimate, compare them with the notice, and discuss unresolved tax or benefits questions with the relevant professional or agency before acting.
For a more focused next step, read the lookback guide, the Part B and Part D comparison, or the MFS guide. Each addresses a different source of confusion that a single headline premium cannot resolve.