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.

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 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.

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. If the beneficiary is a high earning California resident still working in the 32% federal bracket (which begins at $201,776 for single filers and $403,551 for joint filers in 2026) and pays California’s 9.3% state rate, the combined marginal rate on inherited dollars sits north of 41%.

Run the cumulative tax over 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 of the inheritance disappears to income tax if the heir does nothing strategic.

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. IRMAA premiums in 2026 are based on 2024 income. The Part B surcharges run from $81.20 to $487 per month per person, with Part D surcharges 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 never recover. A couple just above the first IRMAA threshold pays roughly $2,300 more per year in combined Part B and Part D premiums compared to staying below the line. These costs compound over multiple years if distributions are not carefully timed.

Bracket Smoothing Is the Whole Game

The strategy is to take partial distributions every year. Front load withdrawals in years when the heir is still working only if those dollars stay inside the 24% bracket, which tops out at $201,775 for singles and $403,550 for joint filers in 2026. If retirement is planned for year 5, defer the heavier withdrawals to those lower bracket years between retirement and the start of the beneficiary’s own Social Security and RMDs.

A few rules that close off common workarounds:

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 is to convert the heir’s own pre tax accounts in low income years to make room for future distributions.
2. The 9 month disclaimer window. A beneficiary can disclaim the inheritance within 9 months, passing the account to the contingent beneficiary. This move is worth considering 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 use their own RMD schedule. Adult children and other non spouse heirs cannot.
4. Charitable offset after age 70 and a half. Once the heir reaches 70½, qualified charitable distributions from their own IRA can offset other taxable income, though QCDs are not permitted from an inherited account before that age. The 2026 QCD limit is $111,000 per person.

What to Do This Week

Confirm 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. Build a year by year distribution schedule that targets the top of the 24% bracket and avoids the next IRMAA tier two years forward.

If you inherited in 2020 through 2023, you are now 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 your deadline. A beneficiary who inherited in 2022 must empty the account by December 31, 2032, and must take 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 planning fee for a CPA who models multi year bracket and IRMAA scenarios pays for itself several times over. The stakes are too high to wing this on intuition.

Editor’s note: This article was updated to reflect 2026 federal tax brackets and IRMAA surcharge figures, the enforcement of annual RMDs starting in 2025 following the IRS waiver period, the current 25% penalty structure for missed distributions, and the 2026 QCD limit of $111,000.