IRMAA-Aware Roth Conversion Calculator (2026)

For Medicare-eligible retirees, Roth conversions can trigger IRMAA surcharges — up to $13,872/year extra for a couple — that hit two years later. This calculator finds your conversion sweet spots: the maximum you can convert before each IRMAA cliff, and the scenarios where crossing a tier is still worth it.

The IRMAA cliff: why $1 over the line costs $1,148/year per person

Unlike income tax brackets (which only apply incrementally to income above the threshold), IRMAA is a cliff surcharge. Cross $218,000 MAGI as a married couple and you owe the full Tier 1 surcharge on all your Medicare premiums — not just the excess. The extra dollar of conversion income can cost a couple $2,296/year.

The IRMAA cliffs fall at completely different income levels than tax bracket thresholds, so the right Roth conversion amount isn't simply "fill the 22% bracket." It's often "fill to whichever comes first — the next tax bracket or the next IRMAA tier."

2026 IRMAA tiers (based on 2024 MAGI)

Source: Kiplinger — 2026 Medicare IRMAA Brackets and Surcharges. Base Part B premium: $202.90/month.

When crossing an IRMAA tier is still worth it

IRMAA is a temporary cost — it applies only while your MAGI stays above the threshold. A conversion is a one-time income event. If you convert $50,000 over an IRMAA tier in 2026, the surcharge applies to 2028 premiums only (assuming your income drops back below in 2027). The break-even is usually straightforward:

• Cost of crossing the tier: Tier 1 surcharge × 1 year × number of enrollees (e.g., $2,296 for a couple)
• Tax savings from the conversion: conversion amount × (expected future bracket − current bracket)

Example: $50,000 converted above IRMAA Tier 1, saving 10 points of bracket (22% now vs. 32% at RMD) = $5,000 in lifetime tax saved vs. $2,296 one-year IRMAA hit. Net: +$2,704. In most bracket-differential scenarios, crossing one tier is justified.

What's usually not justified: a multi-year conversion plan that keeps you in Tier 2 or higher for 5–8 years. Cumulative IRMAA at $5,770/yr per couple adds up quickly.

The two-year lookback trap for new retirees

IRMAA for 2026 is based on your 2024 MAGI. If you retired in 2024 but had W-2 income for most of that year, your 2026 Medicare premiums may be in IRMAA territory even with zero conversions. Once you're in IRMAA anyway, crossing to the next tier becomes the only relevant comparison — not "should I avoid IRMAA" but "should I pay Tier 2 instead of Tier 1 for one year."

File SSA Form SSA-44 if a life event (retirement, loss of a spouse's income, business sale) reduced your current income below what your 2024 return shows. SSA can recalculate IRMAA using current-year income.

Why IRMAA planning requires multi-year modeling

The optimal Roth conversion strategy coordinates:

• IRMAA thresholds (two-year lookback means decisions made this year affect premiums two years from now)
• Tax bracket boundaries (which are on taxable income, not MAGI)
• Social Security income (which stacks on top of conversion income)
• State income taxes (California and New York effectively add 9–13% to the cost of conversions)
• RMD trajectory (how large will forced withdrawals be at 73, 75, 80?)

A spreadsheet can handle one year. A specialist advisor runs the full 10-year model — which years to convert heavily, which years to hold back, and when the lifetime NPV tips decisively one way.