What Happens to a $900,000 401(k) When the Owner Dies and the Beneficiary Falls Under the New 10 Year Rule

A 65 year old who just inherited a $900,000 401(k) from a parent who died at age 75 faces a tax bill most beneficiaries never see coming. The stretch IRA, the estate planning move that let prior generations spread inherited account withdrawals over their own life expectancy, is gone for non-spouse heirs. In its place sits the SECURE Act 10 year rule, effective for deaths after 2019, and final IRS regulations published in July 2024 that made the math considerably worse for most heirs.

The parent died after their required beginning date for RMDs, so the heir cannot wait until year 10 and withdraw everything at once. The final regulations confirm that annual RMDs are mandatory during years one through nine, with the full remaining balance due by December 31 of year 10. The IRS waived enforcement of those annual distributions from 2021 through 2024 while the rules were being finalized. Starting with the 2025 tax year, annual RMDs from inherited accounts became fully enforced, and the 25% penalty for missed withdrawals (reducible to 10% if corrected within two years) now applies in full.

The Tax Bomb in Plain Dollars

Assume the inherited 401(k) earns a 6% blended return inside the account. By year 10, cumulative distributions plus the residual balance approach roughly $1.6 million of taxable income spread across the decade. Consider a high-earning California resident who is still working in the 32% federal bracket. Per the IRS, that bracket begins at $201,775 for single filers and $403,550 for joint filers in 2026. Add California’s 9.3% state rate, and the combined marginal rate on inherited dollars sits above 41%.

Run the cumulative tax across the full 10 years and the bill lands somewhere in the $375,000 to $450,000 range, a 40% to 50% haircut on the net inheritance. The exact number depends on growth and bracket placement, but the order of magnitude is the story: roughly half the inheritance can disappear to income tax if the heir takes no strategic action.

Why the IRMAA Cliff Matters

The 65 year old beneficiary is also a Medicare enrollee. Every distribution dollar lands in modified adjusted gross income and feeds the two-year IRMAA lookback. For 2026, IRMAA premiums are determined by 2024 income, with surcharges beginning at $109,000 MAGI for single filers and $218,000 for joint filers. The Part B surcharges run from $81.20 to $487.00 per month per person, with Part D surcharges of $14.50 to $91.00 per month layered on top.

Pulling a single large distribution in the wrong year can push a retiree two or three IRMAA tiers higher for the following year, adding thousands in premium surcharges that persist. A couple crossing into the first IRMAA tier pays approximately $2,300 more per year in combined Part B and Part D premiums compared to staying below the threshold. Because the surcharge is a cliff system, a single dollar over the limit triggers the full tier premium with no phase-in, and the costs compound over multiple years if distributions are not carefully timed.

Bracket Smoothing Is the Whole Game

The core strategy is to take partial distributions every year rather than lumping income into a few years. Front-load withdrawals in years when the heir is still working only if those dollars remain inside the 24% bracket, which runs from $105,700 to $201,775 for single filers and $211,400 to $403,550 for joint filers in 2026. If retirement is planned for year five, defer heavier withdrawals to the lower-bracket years between leaving work and the start of the beneficiary’s own Social Security and RMDs. That window is often the most tax-efficient stretch of the entire decade.

A few rules close off common workarounds that heirs often assume are available:

1. No Roth conversion on the inherited balance. The IRS does not permit converting an inherited non-spouse 401(k) or IRA to a Roth. The only Roth path available is converting the heir’s own pre-tax accounts during low-income years, which frees up room in future brackets for the inherited distributions.
2. The 9 month disclaimer window. A beneficiary can disclaim the inheritance within 9 months of the owner’s death, passing the account to the contingent beneficiary. This option is worth evaluating carefully if a lower-bracket sibling or a grandchild is next in line.
3. Spouses get different treatment. A surviving spouse can roll the account into their own IRA and draw down under their own RMD schedule. Adult children and other non-spouse heirs do not have this option.
4. Charitable offset after age 70 and a half. Once the heir reaches 70½, qualified charitable distributions from the heir’s own IRA can offset other taxable income. QCDs are not permitted from an inherited account until that age. The 2026 QCD limit is $111,000 per person, up from $108,000 in 2025. Notably, QCDs became more valuable in 2026 under changes introduced by the One Big Beautiful Bill Act, which restricted itemized charitable deductions for high earners, making the direct IRA-to-charity transfer a superior route for many retirees.

One additional tool deserves mention: the SSA-44 life-changing event appeal. If the beneficiary’s income drops significantly after the IRMAA lookback year, filing Form SSA-44 with income documentation can prompt the Social Security Administration to use a more recent, lower-income year for the IRMAA calculation, potentially eliminating or reducing premium surcharges for that year.

What to Do This Week

Start by confirming the decedent’s required beginning date status with the plan administrator. That single fact determines whether annual RMDs are required during the 10-year window or whether the beneficiary can choose the timing of all withdrawals. With that confirmed, build a year-by-year distribution schedule that targets the top of the 24% bracket and avoids crossing the next IRMAA tier two years forward.

If you inherited in 2020 through 2023, you are already mid-window. The 10-year clock started the year after death, and the IRS waiver for missed RMDs in 2021 through 2024 did not extend the final deadline. A beneficiary who inherited in 2022 must empty the account by December 31, 2032, and was required to begin taking annual RMDs starting in 2025 if the decedent had reached their required beginning date.

If projected lifetime taxes on the inheritance exceed $100,000, the cost of engaging a CPA to model multi-year bracket and IRMAA scenarios is almost certainly worthwhile. The math is complex, the penalty for missed distributions is steep, and the window for corrective action narrows every year.

Editor’s note: This pass corrected the 2026 federal tax bracket thresholds throughout: the 24% bracket runs from $105,700 to $201,775 for single filers and $211,400 to $403,550 for joint filers, while the 32% bracket begins at $201,775 for singles and $403,550 for joint filers, per IRS Revenue Procedure 2025-32. The 2026 IRMAA entry threshold ($109,000 for singles, $218,000 for joint filers) and Part D surcharge range ($14.50 to $91.00 per month) were also added, and context was incorporated on the One Big Beautiful Bill Act’s effect on QCD planning and the SSA-44 appeal process for IRMAA reduction.

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