The 401(k) Millionaire's Tax Problem: More Savings, More Taxes

The Math on What RMDs Actually Look Like

Required Minimum Distributions are calculated by dividing your prior December 31 account balance by the IRS Uniform Lifetime Table life expectancy factor for your age. At age 73, that factor is 26.5. The math at different balance levels: A $1 million balance at 73 generates a first-year RMD of $37,736. That is $37,736 in fully taxable ordinary income added to Social Security, pension, and any other retirement income. A $2 million balance at 73 generates a first-year RMD of $75,472. Combined with $40,000 in Social Security (85% taxable) and $15,000 in other income, total gross income exceeds $124,000 - firmly in the 22-24% federal bracket and above the first IRMAA tier for married filers. A $3 million balance at 73 generates a first-year RMD of $113,208. For a married couple with modest Social Security income, total retirement income from all sources easily exceeds $170,000 - potentially triggering IRMAA tier three and a 22-24% federal bracket on most of that income. These numbers do not stay flat. The distribution factor shrinks every year. By age 80, the factor drops to 20.2, meaning a $2 million account forces $99,010 in mandatory withdrawals. By age 85, the factor is 16.0, and the same $2 million account forces $125,000 in annual distributions if it has continued growing. The mandatory taxable income climbs every year for the rest of your life. The 401(k) millionaire who saved diligently and assumed a comfortable retirement may be surprised to find they are in the same or higher tax bracket in retirement than they were during their peak earning years - with no flexibility to reduce the mandatory income and no way to turn off the distribution requirement.

IRMAA Is Nearly Guaranteed Above $1 Million

The IRMAA surcharges on Medicare Part B and Part D premiums are designed for higher-income retirees. In 2026, the IRMAA thresholds begin at $109,000 MAGI for single filers and $218,000 for married filers. For a 401(k) millionaire with $1.5 million in tax-deferred assets, the first-year RMD is approximately $56,604. Add $35,000 in Social Security (85% taxable = $29,750 in taxable SS), and taxable income before deductions exceeds $86,000. After the $32,200 standard deduction, taxable income is approximately $54,000 - safely below IRMAA for a married couple. But by age 80, with a growing account balance, the same couple's RMD has risen to $75,000 or more. Their total income calculation now pushes MAGI toward and potentially above the $218,000 married IRMAA threshold for the second tier. One dollar above that threshold adds $202.90 per month per person in Part B surcharges alone - $4,870 per year for both spouses. For the 401(k) millionaire with $2 million or more in tax-deferred assets, IRMAA exposure is virtually certain by the mid-70s. The surcharges compound the tax burden significantly. In 2026, a married couple in the second IRMAA tier pays an additional $203 per person per month in Part B premiums plus Part D surcharges. Across both spouses, that is over $4,800 per year in Medicare surcharges that would not exist with lower income - surcharges that grow if income continues to rise with the account balance. The IRMAA brackets have been adjusted for inflation in recent years, which helps. But the fundamental relationship between large tax-deferred balances, escalating RMDs, and IRMAA exposure remains structurally consistent.

The RMD Tax Cost Over 20 Years

Looking at the cumulative tax cost of large RMDs over a 20-year retirement illustrates the full scope of the issue. For a single retiree with $2 million in a traditional IRA at age 73, assuming 5% annual account growth and using the Uniform Lifetime Table factors, the cumulative RMDs from age 73 to 92 total approximately $2.3 million. At an average effective federal tax rate of 22% on those distributions (which is modest given the income levels involved), total federal income taxes paid on RMDs over 20 years approach $500,000. That is $500,000 paid to the IRS from an account that was built to fund the retiree's own expenses - not a tax bill paid during earning years on wages, but a bill that follows the retiree throughout their entire retirement, growing larger each year, until the account is either depleted or the retiree dies. For heirs who inherit the remaining balance, the tax burden continues. Under the SECURE Act's 10-year rule, adult children must distribute the inherited IRA within 10 years. At the heirs' income levels - which are often at their own peak earning years when they inherit in their 40s or 50s - the effective tax rate on those distributions can be 24-32%. The total generational tax cost on a $2 million IRA can approach or exceed 40% of the account value when federal income taxes on both the owner's RMDs and the heirs' inherited distributions are combined.

The Pre-Emptive Roth Conversion Strategy

The most effective mitigation for the 401(k) millionaire's tax problem is Roth conversions made during the years before RMDs begin - particularly in the window between retirement and age 73 when income is typically lower. For a 401(k) millionaire who retires at 63 with $1.5 million in tax-deferred accounts, the 10-year window before RMDs begin at 73 is an opportunity to convert $80,000 to $100,000 per year from traditional to Roth at the 22% federal tax rate. Over 10 years, converting $900,000 to $1 million at 22% costs approximately $198,000 to $220,000 in federal income taxes paid now. In exchange, the future traditional IRA balance at 73 is dramatically smaller - perhaps $600,000 to $800,000 rather than $2 million. First-year RMDs on $700,000 are approximately $26,415 rather than $75,472. The Social Security taxation is lower, IRMAA exposure may be eliminated or reduced by a tier, and the blended marginal rate on retirement income drops substantially. The Roth balance, meanwhile, has grown tax-free through the conversion years and continues compounding without RMD obligations. The retiree has flexibility to draw on it in high-income years to avoid bracket spikes and leave it to heirs as a tax-free inheritance. The conversion strategy does not make sense for everyone - it requires discipline to pay significant taxes now for benefits that arrive years later, and it must be carefully modeled against IRMAA thresholds during the conversion years. But for 401(k) millionaires who will face substantial mandatory income in their 70s and 80s, pre-emptive conversion is often the highest-value tax planning decision available.