IRMAA Lookback Planner
Medicare charges higher Part B and Part D premiums to beneficiaries whose income exceeds certain thresholds — and it uses your tax return from two years prior to set those premiums. A Roth conversion you execute today will not affect your premiums this year, but it will affect them two years from now. This planner inputs your current modified adjusted gross income (MAGI) and a proposed Roth conversion amount to show which IRMAA tier you land in for the lookback year, the annual premium surcharge cost per person, and whether your conversion is close enough to a tier boundary that trimming it slightly would avoid the cliff entirely. Cited to SSA IRMAA tables (42 CFR §408.2), Medicare.gov Part B and Part D premium documentation, and 2026 IRMAA thresholds. Not tax advice — consult a CPA, Enrolled Agent, or Medicare specialist before executing any conversion.
Tier 0 on $200,000 MAGI, per person/year
Tier 1 on $250,000 MAGI
base MAGI + conversion
convertible before the next cliff
Converting $50,000 pushes your MAGI from Tier 0 into Tier 1, adding $1,052.40 of IRMAA surcharge per person for 2027 premiums. The whole-tier jump applies to the entire premium, not just the dollars over the line.
The highlighted bar is the tier your conversion lands you in; the blue bar is your current tier. The gap between the two is the surcharge increase you pay, per person, in 2027.
| Tier | MAGI floor | Part B / mo | Part D / mo | Annual |
|---|---|---|---|---|
| Std (0) ◀ current | $0 | $0.00 | $0.00 | $0.00 |
| 1 ◀ after | $212,000 | $74.00 | $13.70 | $1,052.40 |
| 2 | $266,000 | $185.00 | $35.30 | $2,643.60 |
| 3 | $334,000 | $295.90 | $57.00 | $4,234.80 |
| 4 | $400,000 | $406.90 | $78.60 | $5,826.00 |
| 5 | $750,000 | $443.90 | $85.80 | $6,356.40 |
2026CMS figures — thresholds key off MAGI from two years prior. Verify current-year amounts. Surcharges are IRMAA only (above the standard base premium) and per person.
View the TypeScript implementation on GitHub: packages/calc/src/irmaa-lookback.ts · view tests
What this means
IRMAA is the cost retirees most often discover too late, because of the two-year delay between the income that triggers it and the premium bill that arrives. A Roth conversion you run this year is invisible to this year’s Medicare premiums — and then, two years on, it can quietly raise them. The question is never just “how much tax does the conversion cost?” but “does it cross an IRMAA tier, and what does that step cost per person?”
The shape of the surcharge matters more than its size. IRMAA is a step function, not a slope: the dollar that carries you over a threshold doesn’t add a few cents of surcharge, it re-prices your entire Part B and Part D premium for the full year. That is why the headroom number — the dollars of MAGI you have before the next cliff — is the most useful figure on this page. It is your conversion budget if your goal is to stay under the line.
In my experience, the single most valuable thing this planner does is make the cliff legible before the conversion happens. I’ve found that people anchor on the income-tax bill and never see the IRMAA step waiting two years out. I’ve seen a planned conversion sized to land $1,200 under a threshold instead of $2,000 over it — the same Roth benefit, minus a four-figure premium surprise — once the lookback was drawn out as a bar chart rather than buried in a footnote.
Worked example
Take a married-filing-jointly couple with $200,000 of base MAGI in 2025, considering a $50,000 Roth conversion. On the 2026 MFJ schedule, $200,000 sits in the standard (no-surcharge) tier— the first MFJ surcharge floor is $212,000, so their base IRMAA surcharge is $0.00. They have $12,000 of headroom before the first cliff.
Add the conversion and MAGI rises to $250,000, which clears the $212,000 floor and lands in MFJ Tier 1. The Tier 1 surcharge is ($74.00 + $13.70) × 12 = $1,052.40per person for the year. Because the base was $0, the conversion’s IRMAA impact is the full $1,052.40 increase— and since IRMAA is per person, an MFJ couple with both spouses on Medicare pays it twice (about $2,105 at the household level) in their 2027 premiums, two years after the 2025 conversion.
The planning move is visible the moment you see the headroom: converting $11,999 instead of $50,000would keep MAGI at $211,999 — still the standard tier, still $0 of IRMAA. If the long-term Roth benefit justifies the larger conversion, you cross the cliff knowingly; if not, you size the conversion to the headroom and revisit next year. Either way, this is an estimator — verify current-year CMS figures and consult a CPA or Enrolled Agent before converting.
Frequently asked questions
Estimate of the IRMAA Medicare surcharge impact of a conversion via the 2-year lookback — not tax or medical advice. Verify current-year CMS figures. Consult a CPA or Enrolled Agent before executing any conversion.