An IRMAA estimate can be correct and still look different from the total taken from a Social Security payment or charged by a drug plan. The usual reason is that several amounts are being described with the word “premium.” Part B's standard premium, Part B IRMAA, an actual Part D plan premium and Part D IRMAA are distinct. Keeping them on separate lines makes comparisons easier and prevents a benchmark or an unknown plan cost from becoming a fictional bill.
Build the Part B side first
For full Part B coverage, this calculator starts with the published standard monthly premium for the selected premium year. It then adds the applicable monthly Part B income surcharge for the beneficiary's tier. In 2026, the standard premium is $202.90. In the first ordinary surcharge tier, the Part B addition is $81.20, producing a modeled full Part B monthly total of $284.10 when that standard amount applies.
The word “full” matters. Special immunosuppressive-drug-only Part B coverage has a different published schedule and is outside this calculator. Late-enrollment penalties, adjustments to an individual's actual withholding and Medicare Advantage premium reductions are also not modeled. If a notice includes one of those items, compare like with like before deciding the statutory table is wrong. A source-linked planning amount should not be advertised as a guaranteed match to every individual payment deduction.
Treat the drug-plan premium as a separate input
Part D IRMAA is the statutory income-related addition for prescription drug coverage. It does not replace the premium charged by a person's actual drug plan. A plan may advertise a zero-dollar premium while an affected enrollee still owes Part D IRMAA. Conversely, a plan with a positive premium can charge that amount even when the beneficiary is below the first income threshold and owes no IRMAA.
The national Part D base beneficiary premium is another distinct concept. It is a statutory benchmark, not a universal plan quote. The portal displays that benchmark as reference information and never fills an unknown plan premium with it. When you do not know the actual plan amount, leaving the field blank is the accurate choice. An incomplete total with an explained missing input is more useful than a complete-looking total built from the wrong number.
Work through a modest example
Consider an invented 2026 individual in the first ordinary surcharge tier with both components active for a full year. The monthly income additions are $81.20 for Part B and $14.50 for Part D. Together, those income additions are $95.70 per covered month. Across twelve months, the annual IRMAA is $1,148.40. That annual surcharge is different from the standard Part B premium and different from the person's total Medicare spending.
If the same person has an actual drug-plan premium, it belongs on its own line. Adding it changes the known premium-cost total, but it does not change the statutory income tier or the IRMAA amount. If the plan premium is unknown, the surcharge can still be calculated; the complete Part D cost cannot. Keep the label “annual IRMAA” attached only to the income-related additions, rather than using it for standard premiums or plan charges.
Apply coverage month by month
Part B and Part D can begin or end in different months. An annual estimate should therefore apply each component only in its own active window. For example, starting Part B in July and Part D in October does not produce twelve months of either charge. Nor does it produce the same combined amount in every calendar month. January may have no modeled charge, July may have Part B only, and October may include both components.
This distinction becomes even more important in a household. One spouse's Part B months can overlap with, precede or follow the other spouse's coverage. A single “household monthly bill” made by adding unrelated peak monthly amounts can describe a month that never occurs. The portal instead shows calendar-month costs and a range where costs vary. The annual result is the sum of the actual modeled months, not an annual average disguised as a monthly obligation.
Check each beneficiary independently
When spouses file jointly, the joint return can supply the MAGI used for both enrolled people. That does not merge them into one assessed beneficiary. Each person's Part B and Part D participation still matters. If only one spouse has drug coverage, doubling the first spouse's combined surcharge overstates the household's Part D amount. If spouses file separately, their own returns may place them in different tiers as well.
Use the person-level breakdown to inspect which charge belongs to whom. Check the filing classification, income measure, coverage windows and known plan premiums. If one spouse's actual government determination differs because of an approved adjustment or another exception, do not silently force that difference into a shared household assumption. Separate estimates may be necessary to describe different administrative situations accurately.
Reconcile an estimate with a real statement
Create a small reconciliation with separate lines for standard Part B, Part B IRMAA, Part D IRMAA, the actual drug-plan premium and any unmodeled items. Then compare the time period. A statement may include an adjustment or collection arrangement that is not a simple single-month expense. A difference in cash collection does not by itself prove that the underlying annual statutory surcharge is incorrect.
Keep the original statement and the planning report together. The report explains the selected rates, source dates, covered months and omitted plan information; the statement establishes what the agency or plan actually requested. This method helps you ask a precise billing question instead of arguing over an ambiguous word. For income classification, continue with IRMAA fundamentals; for household edge cases, read married filing separately.