What your 2024 return does to your 2026 Medicare premium.

What this worksheet does and doesn't do

• Nothing is saved or transmitted. Figures live only in this browser tab and disappear when it closes — safe to use with client data, but reopen it fresh for each person.
• Self-employment tax is 15.3% on 92.35% of net profit, with the 12.4% Social Security portion stopping at the wage base and coordinated against any W-2 Social Security wages entered. Half of it is deducted. The 0.9% Additional Medicare Tax is excluded — it isn't deductible and doesn't touch AGI.
• Taxable Social Security follows the Form 1040 benefits worksheet. Per those instructions, student loan interest is not subtracted when computing provisional income, so it's excluded from that step but still reduces AGI.
• The health insurance deduction is capped at net profit less the SE tax deduction less retirement contributions. If the entry exceeds that, the worksheet caps it and says so.
• The QBI deduction is deliberately absent. It sits below the line on Form 1040 line 13 and does not reduce AGI — same for the senior, tips, overtime, and car-loan-interest deductions. None of them help with IRMAA.
• MAGI add-backs beyond tax-exempt interest — excluded foreign earned income and housing, excluded savings bond interest used for education, and excluded employer adoption assistance — are rare and not modeled. Add them to "other income" if they apply.
• Bracket boundaries follow CMS's exact wording. The first four tiers are stated as "less than or equal to," but the fifth is "less than $500,000" ($750,000 joint, $391,000 MFS) — so a MAGI of exactly $500,000 falls in the top tier, not the one below it. The worksheet tracks that distinction rather than assuming every boundary is inclusive.

Where the figures come from

• Part B premium, both IRMAA tables, and the Part D adjustment amounts — CMS, 2026 Medicare Parts A & B Premiums and Deductibles, released 14 November 2025. Standard Part B is $202.90/month; the Part B annual deductible is $283.
• Social Security wage base of $184,500 — SSA 2026 COLA fact sheet. Editable above in case of a later correction.
• Benefit taxability base amounts ($25,000 single/HoH/QSS and MFS-lived-apart, $32,000 joint, $0 MFS-lived-with-spouse) — IRS. The second-tier amounts of $34,000 and $44,000 are fixed by statute at IRC §86(c)(2) and are not inflation-indexed.
• One discrepancy worth knowing about. SSA's Medicare premiums page lists the top married-filing-separately adjustment as $487.90, while the CMS fact sheet — and SSA's own individual table on the same page — give $487.00. This worksheet uses the CMS figure. The gap is 90 cents a month and only affects MFS filers above $391,000, but if that is the filer in question, confirm against the determination letter.

Using this for an appeal

SSA sets the 2026 adjustment from the 2024 return. To substitute a more recent year's estimate you file Form SSA-44, which requires one of the life-changing events SSA enumerates: you married, divorced, or were widowed; you or your spouse stopped working or reduced hours; you or your spouse lost income-producing property through a disaster or other event beyond your control; you or your spouse experienced a scheduled cessation, termination, or reorganization of an employer's pension plan; or you or your spouse received a settlement from a current or former employer arising from that employer's closure, bankruptcy, or reorganization. SSA requires documentation of both the event and the resulting income reduction. A decline in income with no qualifying event behind it is not a basis for relief, however large — confirm the event before doing the arithmetic.