Married filing separately (MFS) gets the harshest IRMAA treatment of any filing status. For 2026, the surcharge starts at just $109,000 (the same as a single filer, and half the $218,000 joint threshold), and there are only three tiers. Income over $109,000 jumps straight into a high tier.
Where single and joint filers climb through six tiers, married filing separately has only three. There is no gradual ramp. Crossing $109,000 lands you directly in a high tier.
| 2024 income (MAGI) | Part B / mo | Part D / mo |
|---|---|---|
| $109,000 or less | $202.90 | $0.00 |
| $109,001 – $390,999 | $649.20 | +$83.30 |
| $391,000 or more | $689.90 | +$91.00 |
Source: official 2026 CMS/SSA figures (CMS Medicare costs; SSA Pub. 05-10536). Last verified June 2026.
For most filing statuses the surcharge ramps up through six income tiers. Married filing separately collapses that into three: a standard tier, then a single big jump at $109,000, then the top tier at $391,000. The threshold is not doubled the way it is for joint filers (it sits at the single-filer level), so a spouse with moderate income can pay a surcharge they would never face filing jointly.
Couples rarely choose MFS for the IRMAA result. It is usually a side effect of another decision. Common reasons include separating or divorcing during the year, protecting one spouse from the other's tax liability, income-driven student loan repayment calculations, or large medical or miscellaneous deductions that are easier to claim on a separate return. Whatever the reason, the IRMAA cost of MFS is easy to overlook until the premium notice arrives.