A routine 401(k) withdrawal in 2026 could quietly inflate your Medicare premiums by more than $3,500 a year — two years from now, in 2028. That’s how the Income-Related Monthly Adjustment Amount (IRMAA) works, and most near-retirees don’t see it coming until the bill arrives.
Medicare uses a two-year lookback rule to set Part B and Part D premiums. Income reported on your 2026 tax return — filed in early 2027 — determines what you pay for Medicare in 2028. A large 401(k) distribution, Roth conversion, or rollover this year doesn’t show up as a premium spike until January 1, 2028. By then, the decision is locked in.
What the 2026 Numbers Actually Look Like
The standard Medicare Part B premium rose to $202.90 per month in 2026 — up $17.90 from $185.00 in 2025, a 9.7% increase. IRMAA surcharges kick in when modified adjusted gross income (MAGI) exceeds $109,000 for single filers or $218,000 for joint filers. Those thresholds increased from $106,000 and $212,000 in 2025, adjusted annually using the CPI-U change through August.
The surcharge structure runs across five tiers. At the first tier — $109,001 to $137,000 for single filers — Medicare tacks on $81.20 per month to Part B and $14.50 per month to Part D, totaling roughly $1,148 in additional annual premiums per person. At the top tier, for individuals earning $500,000 or more, the total monthly Part B premium hits $689.90 — a $487.00 surcharge on top of the base. Combined Part B and Part D surcharges at the maximum reach $578.00 per month, or $6,936 per year.
The jump that catches most retirees off guard is the Tier 1-to-Tier 2 cliff. Crossing from $137,000 into the next bracket costs a married couple an additional $3,181 per year. IRMAA is a hard cliff system — one dollar over the threshold triggers the full surcharge for the entire tier. That single dollar effectively carries a marginal cost in the thousands.
What Counts Toward IRMAA — The Full List
IRMAA is calculated on MAGI, which for Medicare purposes includes traditional IRA and 401(k) distributions (including required minimum distributions), Roth conversions, pension income, capital gains, rental income, taxable Social Security benefits, and — this one surprises retirees — tax-exempt municipal bond interest. Roth IRA distributions, HSA withdrawals for qualified medical expenses, and reverse mortgage proceeds do not count.
RMDs deserve special attention. Under SECURE 2.0, the RMD starting age is now 73. Retirees who turned 73 in 2025 and delayed their first RMD to April 1, 2026 must also take their second RMD by December 31, 2026 — two taxable distributions in a single calendar year. That double-distribution can push MAGI across an IRMAA threshold even when annual income otherwise would not.
Inherited IRA beneficiaries subject to the SECURE Act’s 10-year rule face a similar risk. Those who inherited accounts after 2019 may have deferred distributions through year nine, creating a year-10 spike that can push MAGI two or three IRMAA tiers higher — triggering surcharges that persist for years.
The Widowhood Trap and MFS Penalty
Surviving spouses face an especially sharp exposure. A couple filing jointly under the $218,000 threshold may have been clear of IRMAA entirely. After a spouse’s death, the survivor files as Single — and the bracket threshold drops to $109,000, with no change in household income. Surcharges can appear without any additional spending or distribution decision.
Married filing separately carries its own penalty. Spouses living together but filing separate returns owe $649.20 per month for Part B — more than triple the base — once income exceeds $109,000 and remains below $391,000. Those at or above $391,000 pay $689.90 per month.
The Two-Year Window Still Open for 2026
About 5.1 million Medicare beneficiaries paid Part B IRMAA surcharges in 2025, according to the Medicare Trustees Report — roughly 7% of total enrollees. That number is rising as more retirees reach RMD age with larger pre-tax account balances.
The 2026 IRMAA determination — which set premiums effective January 1, 2026 — was based on 2024 tax returns. That window is closed. But income decisions made between now and December 31, 2026 will set Medicare premiums for 2028. Retirees planning rollovers, large conversions, or first-year RMDs this year should model 2026 MAGI against the $109,000 and $137,000 thresholds before executing any distribution.
If an IRMAA surcharge is triggered by a qualifying life-changing event — a business sale, retirement, divorce, or death of a spouse — a life-changing event appeal is available using SSA Form SSA-44. Beneficiaries have 60 days from receiving their IRMAA determination notice to file. According to the Medicare Rights Center, approximately 50% of appeals are delayed or denied due to documentation errors. The appeal window is strict and the paperwork requirements are precise.
“If it’s not listed, it’s considerably harder to get approved. Then you are fighting an uphill battle.” — Danielle Roberts, co-founder of Boomer Benefits, on IRMAA appeal eligibility
Retirees turning 63 or 64 in 2026 are still in the pre-Medicare planning window — the last years to execute Roth conversions before IRMAA exposure begins. Once Part B enrollment starts, every conversion dollar counts toward the surcharge threshold. Modeling 2026 and 2027 MAGI now, before distributions are locked in, is the only lever available.
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