58-Year-Old With $2.3M 401(k) Cuts Deferrals in Half: Here’s Why Brokerage Accounts Win at High Incomes

A 58-year-old investment banker pulling in $850,000 in W-2 income just cut his traditional 401(k) deferral roughly in half and is steering the difference into his taxable brokerage account.

He already has $2.3 million in a traditional 401(k) and $1.4 million in a brokerage account, and he plans to retire at 62 in a high cost-of-living state. The decision that will drive his retirement outcome over the next four years is which bucket he saves into.

The arbitrage that breaks down at high incomes

Traditional 401(k) deferrals work when the marginal rate today sits well above the marginal rate when that dollar comes back out. For this banker, the gap has collapsed.

His top federal bracket is 32%, and his high-tax state adds roughly 6% in effective marginal tax. That stacks to about 38% on the last dollar deferred. The withdrawal rate is where the math turns against him.

With $2.3 million already inside the plan and four more years of growth ahead, his required minimum distributions starting at age 73 will push ordinary income into the 24% to 32% federal brackets before he touches a dollar voluntarily. Layer in Social Security, deferred comp, and taxable account distributions, and the withdrawal rate looks a lot like the deferral rate. The arbitrage shrinks toward zero. In a state that taxes retirement income heavily, it can go negative.

Why the brokerage account wins the next four years

Every dollar he diverts to a brokerage account is taxed once at his W-2 rate going in. Growth is taxed at long-term capital gains rates, currently 15% to 20% federally, plus the 3.8% net investment income tax at his income level. Compare that against the 24% to 32% federal ordinary rate that will hit every traditional 401(k) dollar he withdraws in retirement, and the brokerage path is competitive on tax and more flexible on access.

Flexibility matters because he wants to retire at 62. Brokerage assets carry no age gate, no 10% penalty, no 59½ rule, and they step up at death. They also fund the bridge years between retirement and Social Security, when he will run aggressive Roth conversions from the existing $2.3 million traditional balance.

The mechanic he is using

He kept enough traditional 401(k) deferral to capture the full employer match. Skipping a match is leaving cash compensation on the table at any tax rate. He reduced his deferral to roughly $12,500, redirected about $12,000 of would-be deferral into a brokerage account holding tax-managed index funds and a direct indexing sleeve for ongoing tax-loss harvesting, and is evaluating whether the portion still going into the plan should flip to the Roth 401(k) option.

The macro backdrop reinforces the move. The 10-year Treasury sits at about 4.4%, headline PCE inflation reaccelerated to 3.5% in March, and core PCE is back to 3.2%. Real, after-tax returns fund a 30-year retirement. A 38% wrapper on the way in followed by 28% on the way out eats compounding.

The IRMAA cliff he is planning around

Once Medicare starts at 65, every additional dollar of modified adjusted gross income can trigger IRMAA surcharges with a two-year lookback. His Roth conversion plan for the 62-to-72 window is sized to fill the 24% bracket without crossing the highest IRMAA tiers, which can add several thousand dollars per person per year in Part B and Part D premiums. Running those conversions requires cash from outside the IRA to pay the tax, and that cash lives in the brokerage account he is now feeding.

What to do if your numbers look like his

1. Run the deferral-versus-withdrawal rate comparison honestly. Project your RMD at 73 on your current 401(k) balance compounded at 6% to 7%, add Social Security and any pension, and locate that total on the current IRS brackets. If your retirement marginal rate lands within five points of your working marginal rate, traditional deferral above the match is no longer obvious.
2. Keep the match, redirect the overflow. Capture every dollar of employer match in the 401(k), then route additional savings into a taxable brokerage account using tax-managed funds or direct indexing. If your plan offers a Roth 401(k), consider it for the portion that stays in the plan.
3. Map your Roth conversion window now. The years between retirement and age 73 are the most valuable tax real estate you will ever own. If your projected RMDs will push you into the 24% bracket or higher, every dollar converted in a lower bracket during that window pays for itself, and the cash to pay the conversion tax should already be in your brokerage account.