Medicare sets each year's premium using the tax return you filed two years earlier, and the income-related surcharge (IRMAA) jumps in steps rather than sliding. Go one dollar over a threshold and you pay the full step for twelve months, long after the conversion itself.
With $70,000 of other income, converting $39,000 adds nothing to your premium. Converting $40,000 adds $1,148 a year. The extra $1,000 that crossed the line is by far the most expensive part of the conversion.
A single filer, age 63, with $70,000 of other income. The surcharge is what one person pays for the year that Medicare bases on this return.
| Converted | MAGI | Surcharge / year | Added |
|---|---|---|---|
| $0 | $70,000 | $0 | — |
| $25,000 | $95,000 | $0 | — |
| $39,000 | $109,000 | $0 | — |
| $40,000 | $110,000 | $1,148 | +$1,148 |
| $67,000 | $137,000 | $1,148 | — |
| $68,000 | $138,000 | $2,885 | +$1,736 |
| $100,000 | $170,000 | $2,885 | — |
| $135,000 | $205,000 | $4,620 | +$1,735 |
Plan year 2026. Per beneficiary, per year.
| MAGI over $109,000 | +$1,148 |
| MAGI over $137,000 | +$1,736 |
| MAGI over $171,000 | +$1,735 |
| MAGI over $205,000 | +$1,735 |
| MAGI over $500,000 | +$581 |
| MAGI over $218,000 | +$1,148 |
| MAGI over $274,000 | +$1,736 |
| MAGI over $342,000 | +$1,735 |
| MAGI over $410,000 | +$1,735 |
| MAGI over $750,000 | +$581 |
A conversion window usually runs several years, and the surcharge lands on whichever year crossed a threshold. The planner runs the whole window, shows which year caused the surcharge, and shows what the conversion did to the rest of your tax return.
The income-related monthly adjustment amount (IRMAA) added to Medicare Part B and Part D premiums, priced off modified adjusted gross income from two years earlier. Figures are the annual surcharge for one beneficiary.
Medicare prices each year off the return filed two years before, so a conversion at 63 sets the premium at 65.
A married couple where both are enrolled pays the surcharge each, so double these figures. Thresholds are indexed annually, and a one-off event can be appealed with form SSA-44 only for a listed life-changing event — a Roth conversion is not one of them.
Calculated by the same code the planner uses, and checked against it by a test.
This is a projection based on stated assumptions. It is not financial or tax advice.