The $39,200 Tax Cost That Saves $100,000 Later: A 401(k) Strategy for 60-Year-Olds

A single filer at 60, $250,000 of W-2 income, $2.1 million already stacked in a traditional 401(k), five years from retirement. The default move is to keep deferring at the 32% bracket and take the deduction. For pre-retirees with this profile, the better answer is to flip the next five years of contributions into the Roth 401(k) bucket and pay the tax now. The reasoning rests on a SECURE 2.0 rule change that quietly broke the old playbook, combined with a 2026 mandate that actually removes the choice for high earners.

The Bill She Pays Up Front

Routing the $24,500 annual employee deferral into a Roth 401(k) instead of a pre-tax account costs her roughly $7,840 in additional federal tax each year at the 32% marginal rate, or about $39,200 across five years. That is the real out-of-pocket cost: a larger check to the IRS every year through 2030.

The pre-tax deferral feels like free money because it shrinks today’s bill. In practice it is a loan from the government, repayable at whatever rate applies when she withdraws. For someone who will spend retirement in the 22% to 24% bracket, deferring at 32% can still pencil out. The break-even gets shakier once required minimum distributions, Social Security taxation, and IRMAA Medicare surcharges enter the picture.

Why the Math Flips After 73

Five years of $24,500 contributions compounded at 7% grows to roughly $145,000 by age 65. Left to compound another 20 years through age 85, that balance becomes about $455,000. In a Roth 401(k), every dollar of that $455,000 comes out tax-free after age 59½ with the five-year clock satisfied. In a traditional 401(k), the same $455,000 faces ordinary income tax at withdrawal, costing $100,000 to $110,000 in lifetime tax at a 22% to 24% RMD-era rate.

The upfront cost is roughly $39,200. The avoided tax is closer to $100,000. That gap widens if spending pushes her into a higher retirement bracket. Congress permanently extended the Tax Cuts and Jobs Act bracket structure in July 2025 through the One Big Beautiful Bill Act, which removed the looming rate cliff that once made Roth conversions urgent. The case for going Roth is now structural rather than deadline-driven: convert while you are in a lower bracket, before RMDs force the issue at 73.

The SECURE 2.0 Rule That Changed the Decision

Through 2023, Roth 401(k) balances were subject to required minimum distributions just like traditional balances. IRS Notice 2024-2 implemented the SECURE 2.0 provision eliminating RMDs on Roth 401(k) accounts starting in 2024. The Roth bucket now behaves like a Roth IRA inside the employer plan: it compounds untouched through her 70s and 80s and passes to heirs inside the 10-year tax-free window.

That single rule kills the strongest argument for staying pre-tax. The old playbook assumed both buckets would be force-drained at 73 under the IRS Uniform Lifetime Table. Only the traditional $2.1 million still is. A 73-year-old with a $2.5 million traditional balance faces a first-year RMD of roughly $94,000, calculated by dividing the prior year-end balance by the IRS distribution period of 26.5. That mandatory withdrawal, layered on top of Social Security and any other income, is precisely what trips the 85% Social Security taxation threshold and pushes modified adjusted gross income above the $109,000 IRMAA threshold for single filers, adding at least $1,148 per year in Medicare surcharges at the first tier alone.

Three Moves, In Order

1. Flip the next five years of contributions to the Roth 401(k) sleeve. Confirm the plan offers it. Most large plans now do. The employer match still lands in the pre-tax bucket by default unless the plan has adopted the SECURE 2.0 Roth match election.
2. Route the SECURE 2.0 super catch-up entirely to Roth. Ages 60 through 63 unlock an enhanced catch-up of $11,250 on top of the $24,500 standard deferral for 2026. There is an added reason to do this: starting in 2026, any employee earning more than $150,000 in FICA wages in the prior year is required by law to make all catch-up contributions on a Roth basis. At $250,000 of W-2 income, this person has no pre-tax catch-up option regardless. Paying tax on that $11,250 at the 32% bracket buys outsized Roth growth because the four-year window is short and the compounding runway is long.
3. Map bracket-filling conversions for ages 65 through 72. Once W-2 income stops at retirement and before RMDs begin at 73, the marginal bracket likely drops to 12% or 22%. Converting traditional balances up to the top of the 24% bracket in those years shrinks the future RMD pile at a meaningful discount to the rate she is paying today.

One trap to avoid: a large Roth conversion in any year Medicare premiums are being calculated. IRMAA uses a two-year lookback on modified adjusted gross income, so a $100,000 conversion at 63 can add thousands of dollars in Medicare surcharges at 65. The conversion plan needs to be modeled year by year, not executed in one move.

Editor’s note: This article was updated to reflect the One Big Beautiful Bill Act (signed July 2025), which permanently extended the TCJA individual tax brackets and removed the anticipated rate sunset as a driver of Roth conversion urgency. The article also adds the 2026 mandatory Roth catch-up rule for employees earning more than $150,000 in prior-year FICA wages, which eliminates the pre-tax catch-up option for the $250,000 earner in this scenario. The first-year RMD figure on a $2.5 million balance at age 73 was specified at roughly $94,000 using the IRS Uniform Lifetime Table divisor of 26.5.

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