Quick Read

  • $24,500 annual Roth 401(k) deferral costs $7,840 now but avoids $100,000+ in lifetime RMD taxes.

  • Flip to Roth 401(k) contributions immediately; SECURE 2.0 eliminated Roth RMDs starting 2024.

  • The analyst who called NVIDIA in 2010 just named his top 10 AI stocks. Get them here FREE.

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.

The Bill She Pays Up Front

Routing the $24,500 annual employee deferral into a Roth 401(k) instead of pre-tax 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. She writes a larger check to the IRS through 2030.

The deferral feels like free money because it shrinks today’s bill. In practice it is a loan from the government, repayable at whatever rate Congress sets 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.

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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 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 inflation pushes her into a higher retirement bracket. Core PCE has continued climbing through early 2026, well above the Fed’s 2% target. Tax brackets adjust for inflation slowly; spending power erodes faster.

The SECURE 2.0 Rule That Changed the Decision

Through 2023, Roth 401(k) balances were subject to required minimum distributions exactly 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 near a five-figure sum, layered on top of Social Security and any other income. That stack is what trips the 85% Social Security taxation threshold and triggers IRMAA Medicare surcharges of meaningful monthly Medicare premium surcharges per person.

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 standard deferral. Paying tax on that contribution 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, her 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 discount.

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. Model the conversion year by year.

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