I’m 58, single, and Medicare is still seven years away. It already matters to me, though, because of one rule: the premium I’ll pay at 65 is set by the income on the tax return I file for the year I turn 63. Those are exactly the years I’d want to do Roth conversions. So I built a small IRMAA calculator that answers the narrow question first: given a year’s income, which Medicare surcharge tier does it land in, what does that cost, and how close is the next cliff?
It’s free, there’s no signup, and it runs in your browser. You enter three things and it answers right away.
What the IRMAA calculator asks, and what it tells you
IRMAA stands for income-related monthly adjustment amount. It’s the extra you pay on top of the standard Medicare Part B premium (and on Part D) once your modified adjusted gross income crosses set thresholds. For IRMAA, MAGI is your adjusted gross income plus any tax-exempt interest. Social Security explains the rules on its page on premiums for higher-income beneficiaries, including the 2026 thresholds this tool uses.
The calculator has three inputs: your filing status (single or married filing jointly), your MAGI from two years earlier, and how many people in the household are on Medicare (one or two). Out comes your tier, the extra cost per person per year and per month, the household total, how much more MAGI you can add before the next step, and how much you’d have to cut to drop back to the tier below.
Here are the 2026 thresholds and premiums it runs on. The standard Part B premium in 2026 is $202.90 a month. Each tier applies when MAGI is above the number shown, and the last column is the surcharge only, per person, per year.
| Single MAGI above | Joint MAGI above | Part B / month | Part D extra / month | Extra per year, per person |
|---|---|---|---|---|
| $109,000 | $218,000 | $284.10 | $14.50 | $1,148.40 |
| $137,000 | $274,000 | $405.80 | $37.50 | $2,884.80 |
| $171,000 | $342,000 | $527.50 | $60.40 | $4,620.00 |
| $205,000 | $410,000 | $649.20 | $83.30 | $6,355.20 |
| $500,000 | $750,000 | $689.90 | $91.00 | $6,936.00 |
The last column is just arithmetic: twelve times the Part B premium above the $202.90 standard, plus the Part D extra. I left the standard premium out on purpose. You pay it no matter what your income is, so it isn’t part of what a conversion costs you.
A worked example: $140,000 of MAGI, single
Take a single filer whose MAGI two years ago was $140,000, with one person on Medicare. That’s what the screenshot above shows.
$140,000 is above $137,000 and below $171,000, so it’s tier 2 of 5. In tier 2 the Part B premium is $405.80 a month, which is $202.90 more than the standard $202.90. Add the Part D extra of $37.50 and the surcharge is $240.40 a month. Times twelve, $2,884.80 a year (the calculator rounds it to $2,885).
Then it looks both ways. Up: the next threshold is $171,000, so there’s $31,000 of room before tier 3. Crossing it would raise the surcharge from $2,884.80 to $4,620.00, another $1,735.20 a year. Down: the tier-2 threshold is $137,000, so cutting MAGI by $3,000 drops you to tier 1, where the surcharge is $1,148.40. That saves $1,736.40 a year.
Now look at that last number the way an analyst would. Those top $3,000 of income cost $1,736.40 in Medicare premiums, and that’s before any income tax. That’s a 58% charge on $3,000. A single dollar over $137,000 costs the same $1,736.40. There is no phase-in at all: one dollar over a threshold buys the whole step, for the whole year, for each person on Medicare. For a married couple both on Medicare, crossing the first joint threshold by a dollar costs $2,296.80 a year.
That’s why the calculator reports distances instead of just a tier. Knowing you’re in tier 2 doesn’t tell you much. Knowing you’re $3,000 over the line tells you exactly what to do (if you still control that year’s income, that is).
The two-year lookback is where conversions bite
Medicare sets this year’s premium from the return you filed two years ago. Your 2026 premium comes from your 2024 MAGI. That’s why the input is labeled “MAGI from two years earlier”, and it’s the part people get wrong. You don’t enter this year’s income to see this year’s premium. You enter this year’s income to see the premium two years from now.
For anyone in a Roth conversion window, that changes the order of things. Say I’m 63, single, and my other income puts my MAGI at $90,000. I could convert another $19,000 and land exactly on $109,000, which still pays no surcharge. Convert $19,001 and, at 65, I pay $1,148.40 more for Part B and Part D that year. The conversion happened two years earlier and I’d have half forgotten about it by then. And every conversion after that does the same thing to the premium two years later.
It works the other way too. If your income dropped because of a life-changing event such as retirement, the death of a spouse or divorce, Social Security lets you ask for a lower tier on Form SSA-44. That matters for the first couple of years after you stop working, when Medicare would otherwise be looking at your last full salary.
I have a related cliff in my own near future: before 65 there’s the ACA subsidy, which also reacts badly to conversion income. I wrote up how Roth conversions run into the ACA subsidy cliff separately. IRMAA is the same kind of problem after 65, with a two-year delay.
What this calculator does not do
It’s a one-year lookup, and it’s honest about being one. A few things it leaves out on purpose, and a few it just can’t know:
- It uses the 2026 thresholds and premiums. CMS publishes new figures each year, and until I update the tool, it shows 2026 numbers. Don’t read it as next year’s premium.
- It doesn’t project anything. Thresholds change from year to year, and the calculator only tells you where one MAGI figure lands on the 2026 table.
- It only does single and married filing jointly. Married filing separately has its own chart on the SSA page, and the tool doesn’t cover it.
- It adds the Part D surcharge for everyone. If you don’t have Part D coverage, that piece doesn’t apply to you, so your real number is a bit lower.
- It doesn’t compute MAGI for you. You have to bring the right figure from the right year’s return: AGI plus tax-exempt interest.
- It doesn’t tell you whether crossing a threshold is worth it. Sometimes paying a tier is the right call, because the tax you save by converting now is bigger than the premium.
That last one is the real question, and it can’t be answered one year at a time.
When one year isn’t the question
How big should each year’s conversion be when every dollar pushes a premium cliff two years out? That depends on your brackets, your RMDs later, your Social Security start date and your spending, all at once. I put off modeling IRMAA in my own optimizer for a long time, because cliffs turn a nice linear program into an integer one (and integer programs have a way of running for eighty seconds when you promised yourself sub-second). The story of finally doing it is in how I added IRMAA to my Roth conversion calculator.
In the full Roth conversion optimizer, turn on Medicare & investment-income surcharges under Advanced. It treats each IRMAA tier as the cliff it is, and only pays for a step when the tax saved by converting is worth more than the premium. What you usually see is the solver parking income right at a threshold, year after year, never a dollar over. If you’re still deciding on a ballpark first, how much to convert to a Roth each year covers the bracket side before Medicare enters the picture.
For a quick check of one year, though, the IRMAA calculator is the faster tool. Put in last year’s number, and the year you’re planning, and see how far each one sits from the line.
Things that I use, like, and am affiliated with:
Mint Mobile offers great cell phone service for $15 flat, get $15 off using the link. Get discounted phones with service activation and no contract.
I never spend money before I check Mr Rebates or Rakuten to get cashbacks, rebates, discounts, coupons or cheaper gift cards.