You Get About 10 Quiet Years to Fix Your 401(k). Most People Spend Them Doing Nothing.

Fidelity recently reported a record number of 401(k) millionaires — roughly 769,000 accounts over the seven-figure mark. Every one of those statements looks like a finish line. Almost none of them are.

A traditional 401(k) balance is not entirely yours. It is a joint account with the federal government, and the government has not told you its share yet. It gets to decide later, using whatever tax law exists in the year you withdraw.

The decade nobody uses

For most retirees there is a stretch between the last paycheck and the first Required Minimum Distribution — usually somewhere from the early sixties to age 73 — when taxable income collapses. No salary. Maybe no Social Security yet. Just dividends, interest, and whatever you pull for living expenses.

That is the cheapest tax environment you will ever have again. It is also the only window where you are in charge of how much income shows up on your return. After 73, the IRS writes the withdrawal schedule and you sign it.

Most people spend that window doing the intuitive thing: leaving the pre-tax account alone because touching it means paying tax. Which is true. It also means the balance keeps compounding — and so does the eventual bill.

What the bill actually looks like

Take a $2.6 million pre-tax balance at 74. The RMD alone lands north of $100,000 for the year — before Social Security, before pension income, before dividends. That single forced withdrawal can push a couple into the 24% bracket, drag up to 85% of their Social Security into taxable income, and trip an IRMAA surcharge on Medicare premiums two years later.

None of that is a penalty for doing something wrong. It is the arithmetic of having saved well in the wrong tax bucket.

Filling brackets on purpose

The strategy is unglamorous: in the low-income years, deliberately convert or withdraw just enough from the pre-tax account to fill up a bracket you are comfortable paying — and stop. Not "convert everything." Not "convert nothing." Convert to a line.

Done for eight or ten years, that shifts a large share of a pre-tax balance into a Roth account, where growth is tax-free, there are no RMDs, and heirs inherit without a tax bill attached. Done for zero years, the whole balance arrives at 73 at once, at whatever rate is on the books then.

The lines that make it complicated

• IRMAA. Medicare premiums are set from your return two years back. A large conversion at 63 or 64 is invisible to Medicare. The same conversion at 66 is not.
• ACA subsidies. If you retired before 65 and buy coverage on the exchange, a conversion can cost you premium credits worth more than the tax you saved.
• Capital gains stacking. Conversions are ordinary income and can push long-term gains from the 0% rate into the 15% rate.
• Your heirs' brackets. If the kids are in their peak earning years, the inherited pre-tax account gets taxed at their rate over ten years, not yours.

The uncomfortable part

Voluntarily paying tax you were not required to pay this year feels like losing. That is exactly why the window goes unused. The people who use it are not paying more tax. They are choosing the year, the rate, and the amount, instead of letting a table in an IRS publication choose for them at 73.

If you are between 60 and 72 with a large pre-tax balance, the question worth answering before December is not "should I convert." It is "what is the biggest number I can move this year without crossing a line that costs me more than it saves."

This is general education, not personal tax advice. Bracket math, IRMAA thresholds, and subsidy cliffs are specific to your return — run the numbers with a licensed advisor on our team, alongside your tax preparer, before converting anything.