A $600K Roth Conversion Costs $6,356/Year in Medicare Surcharges — Two Years Later
We ran a single filer’s MAGI from $105,000 to $106,001 through the calculator — a $1,001 difference. Part B premium at $105,000: $185.00/month, the base rate. Part B premium at $106,001: $259.00/month. That’s a $74/month, $888/year jump triggered by crossing one specific dollar amount, not by the size of the income increase itself.
The cliff, not a slope
IRMAA (Income-Related Monthly Adjustment Amount) governs Medicare Part B and Part D premiums for higher-income beneficiaries. Unlike income tax brackets, which only apply a higher rate to the dollars above each threshold, IRMAA applies its entire tier to your whole premium the moment your MAGI crosses the line.
| 2025 Single MAGI | Part B total/mo | Part D surcharge/mo | Annual IRMAA cost |
|---|---|---|---|
| ≤ $106,000 | $185.00 | $0.00 | $0 |
| $106,001 – $133,000 | $259.00 | $13.70 | $1,048.40 |
| $133,001 – $167,000 | $370.00 | $35.30 | $2,643.60 |
| $167,001 – $200,000 | $480.90 | $57.00 | $4,315.80 |
| $200,001 – $500,000 | $591.90 | $78.60 | $5,834.40 |
| > $500,000 | $628.90 | $85.80 | $6,356.40 |
A retiree converting $600,000 of a traditional IRA to Roth in one tax year lands in the top tier — a $6,356.40/year Medicare surcharge, arriving two years after the conversion, on top of whatever ordinary income tax the conversion itself triggered.
Why the two-year lag catches people off guard
The premium you pay in 2025 is based on your 2023 tax return. That lag means a large one-time income event — a Roth conversion, selling a business, a big capital gain — shows up as a Medicare cost surprise two years after the decision, often after the person has already adjusted their spending around what they assumed their fixed costs would be. By the time the IRMAA notice arrives, the income-timing decision that caused it is long past.
Where this framework doesn’t apply
- You’re not on Medicare yet. IRMAA only applies once you’re enrolled in Part B/D, typically starting at 65. A large income year well before then has no IRMAA consequence, though it still affects that year’s regular income tax.
- You just had a life-changing event. Retirement, job loss, divorce, or the death of a spouse qualifies you to file SSA-44 and use your current, lower expected income instead of the two-years-prior default.
- You file married filing separately. That status has its own, much narrower bracket structure — most of the wide “married filing jointly” thresholds don’t apply to it.
- Your income is naturally volatile. A one-time spike reverts the following year, and IRMAA reverts with it two years later — this isn’t a permanent premium increase unless the underlying income stays elevated.
What to actually do
- Check where your current MAGI sits relative to the nearest IRMAA threshold before finalizing a Roth conversion or other discretionary income event.
- If you’re close to a threshold, consider spreading a large conversion across multiple tax years instead of doing it all at once.
- Look at Qualified Charitable Distributions if you’re 70½+ — they reduce MAGI directly rather than through a deduction, sidestepping the IRMAA calculation entirely. See our QCD strategy breakdown for the mechanics.
- If a life-changing event just lowered your income, file SSA-44 rather than accepting the two-years-prior MAGI by default.
- Factor IRMAA into any year you’re also managing Required Minimum Distributions — see what an $800K IRA’s first RMD looks like for how RMD size interacts with MAGI-based cliffs like this one.
Open the Medicare IRMAA Cliff Calculator → and see exactly where your own MAGI lands across all five tiers.