Retirement with a healthy IRA balance can make a large lump-sum withdrawal feel reasonable, whether it’s for a home renovation, a family gift, or a gap-year expense.
What most retirees don’t anticipate is that one distribution can trigger costs far beyond the income tax owed.
Medicare uses a two-year lookback to set premiums, and a single income spike can push monthly Part B costs from $202.90 to as high as $689.90 per person, the Centers for Medicare and Medicaid Services confirmed in its 2026 premium schedule.
The surcharge behind that jump is called the Income-Related Monthly Adjustment Amount, or IRMAA, and it operates on a cliff structure that penalizes retirees for crossing a threshold by even one dollar.
How a large IRA withdrawal triggers Medicare’s IRMAA surcharge
Every dollar pulled from a traditional IRA counts as ordinary income, feeding directly into modified adjusted gross income.
Medicare uses MAGI from two years prior to set current-year premiums, so a large 2024 distribution determines what retirees pay throughout 2026.
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For married couples filing jointly, the first IRMAA tier activates when MAGI exceeds $218,000, with surcharges escalating through five brackets up to $750,000, CMS data show.
The jump to the first tier costs a couple $2,297 per year in added premiums, and moving to the second adds another $3,475, bringing the combined surcharge to $5,772, Taylor Schulte of Define Financial reported in his 2026 IRMAA playbook.
“IRMAA is based on MAGI from two years ago,” Clifford C. Cornell, a financial advisor at Bone Fide Wealth, told Moneywise. “So, a large distribution this year might not impact someone immediately, but two years down the line, those surcharges can show up.”
Social Security taxation compounds the IRA withdrawal problem
The damage from an oversized IRA withdrawal extends beyond Medicare premiums. The same income that triggers IRMAA also determines how much of a retiree’s Social Security benefit becomes taxable.
The IRS calculates provisional income by adding adjusted gross income, tax-exempt interest, and half of the Social Security benefit.
Once that total crosses $25,000 for single filers or $32,000 for joint filers, up to 50% of the benefit becomes taxable. Above $34,000 (single) or $44,000 (joint), the taxable share rises to 85%, according to the Social Security Administration.
Those thresholds have remained unchanged since the 1980s and 1990s, meaning a retiree with moderate income in 2026 can easily find 85% of their Social Security subject to federal tax.
A $40,000 IRA withdrawal on top of Social Security and a pension can push a household past both the taxation threshold and an IRMAA tier simultaneously, creating compounding costs no single line item on a tax return fully reveals.
Required minimum distributions add forced income once retirees hit their RMD age
The risk grows once required minimum distributions begin. Under the SECURE 2.0 Act, RMDs start at age 73 for most retirees, and individuals born in 1960 or later will see that age shift to 75.
The IRS calculates the required amount as a percentage of your year-end tax-deferred account balance, and that percentage increases with age.
On a $1 million traditional IRA, the initial RMD falls in the range of $36,000 to $40,000, and the amount grows each subsequent year, regardless of whether you need the funds for living expenses.
Because RMDs count as ordinary income, they stack on top of Social Security benefits, pensions, and investment income when determining both your tax bracket and your IRMAA tier.
A recent analysis from UBS Wealth Management warned that layered retirement income can push a retiree’s effective tax bracket higher than it was during their peak earning years.
The pre-RMD window between retirement and age 73 offers a planning opportunity
The years between retirement and age 73, when required minimum distributions begin, represent the period when income is typically lowest, and tax brackets are most favorable for strategic action.
Schulte wrote in Define Financial’s IRMAA guide that retirees can reduce future surcharges by spreading Roth conversions across multiple lower-income years rather than completing one large conversion.
Schulte noted that converting portions of a traditional IRA to a Roth during this window shrinks the balance subject to future RMDs, lowering the provisional income that triggers both Social Security taxation and IRMAA costs later.
Wade Pfau, founder of Retirement Researcher, told GOBankingRates that retirees in their 60s who delay Social Security have the best window to run conversions at low rates before required distributions begin.
Roth conversions provide a great opportunity to pay taxes when it can be done at the lowest possible rates. The best window for this is for individuals who retire in their 60s and delay claiming their Social Security benefits until closer to age 70.
“People don’t know what IRMAA is,” Nancy Gates, lead educator and financial coach at Boldin, told Kiplinger. “They could pay three times what everyone else pays for Medicare.”
Qualified charitable distributions offer a separate tool for retirees 70½ or older. The IRS allows up to $111,000 per year in direct IRA-to-charity transfers in 2026, Fidelity’s QCD guidance confirms.
That amount satisfies the RMD requirement without appearing as taxable income, protecting against both Social Security taxation increases and IRMAA tier jumps.
IRMAA’s cliff structure punishes retirees who miss a threshold by one dollar
IRMAA does not work like federal income tax brackets, and crossing a threshold by even one dollar triggers the full surcharge for that entire tier, not just on the excess amount.
A married couple reporting $218,001 in MAGI pays $284.10 per person per month in Part B premiums instead of $202.90, adding roughly $1,950 in annual Part B costs when both spouses are enrolled.
Schulte recommended running a MAGI projection before completing any large transaction to identify which surcharge tier the additional income would trigger, and whether a modest adjustment to the withdrawal amount or timing can avoid crossing the boundary entirely.
Related: Medicare’s costliest gap threatens retirement savings
