Roth headroom finder
How much can you convert before the cliff?
A Roth conversion adds to your MAGI dollar for dollar. Enter your income without the conversion, add what else you expect this year, and see the largest conversion that keeps your Medicare premium where it is two years from now.
Enter your income before the conversion to see your headroom.
Before and after on the cliff profile
The blue dot is your income without the extra items. The dashed arrow shows where they take you.
Why headroom is the number to plan around
Income tax on a Roth conversion rises smoothly: each extra dollar is taxed at your marginal rate. IRMAA does not work that way. It is a set of cliffs, and the moment your modified adjusted gross income passes a limit, the whole next tier applies for the full premium year. For one person on the 2026 brackets, the first cliff at $109,000 costs $1,148 a year in extra Part B and Part D charges. A couple filing jointly pays $2,297 more if both are on Medicare.
Headroom is simply the distance from your income to the top of your current tier. Convert up to that amount and the conversion costs you income tax only. Convert one dollar more and you also pay the higher Medicare premium for a year.
A worked example
Linda is single, already on Medicare, and expects $100,000 of MAGI this year before any conversion. The top of the standard tier is $109,000, so her headroom is $9,000. If she converts $30,000 instead, her MAGI reaches $130,000, she lands in the first IRMAA tier, and her Medicare cost two years later rises by $1,148. Converting $9,000 this year and the rest over the next few years keeps her on the standard premium, as long as her other income stays put.
Count everything that lands in MAGI
Conversions are rarely the only extra income in a year. Capital gains from rebalancing, a required minimum distribution, a large mutual fund distribution in December, or a one-time bonus all count. That is why this tool asks for them separately: your Roth headroom is what is left after the income you cannot move. Qualified charitable distributions are the exception; sent directly from an IRA to a charity, they never enter your adjusted gross income.
Mind the two-year lag
Social Security uses the tax return from two years earlier. A conversion in 2026 sets your 2028 premiums, so the 2026 brackets here are a stand-in: the real 2028 limits will be somewhat higher because they rise with inflation. Testing against the projected 2027 brackets gives a slightly more forgiving view. Leaving a small cushion of a few thousand dollars below the limit protects you from a surprise dividend or a rounding difference.
If you are under 63, a conversion this year does not touch your Medicare premiums at all. That window is one of the best times to convert; the guide on IRMAA planning at 63 explains the timing, and Roth conversions and IRMAA covers multi-year strategies.