Most people spend their working years being told, correctly, to put money in the 401(k). It is good advice. But followed on its own for thirty years, it leaves you with one enormous bucket of money that shares a single feature: every dollar you take out is taxed as ordinary income, at whatever rate applies the year you withdraw it.
That is not a disaster. But it hands the IRS a permanent seat at your retirement table, and there is a better way to sit them down.
The three buckets
Money can live in one of three tax treatments, and the goal of tax diversification is to have meaningful amounts in each:
- Tax-deferred — traditional 401(k) and IRA. You deducted the contribution, the money grows untaxed, and every withdrawal is taxed as income. Eventually the government forces withdrawals through required minimum distributions.
- Tax-free — Roth IRA and Roth 401(k). You paid tax on the way in, and everything after that — growth and withdrawals — is tax-free, with no forced distributions during your lifetime.
- Taxable — an ordinary brokerage account. No special treatment going in, but long-term gains are taxed at lower capital-gains rates, and your heirs may receive a valuable step-up in basis.
Why one bucket is a problem
Picture a retiree with everything in a traditional 401(k). Every dollar of spending is a taxable withdrawal. A large unexpected expense — a new roof, a medical bill — means a large taxable withdrawal, potentially pushing them into a higher bracket and even raising their Medicare premiums two years later. They have no way to take money out without a tax consequence, because they only have one lever.
Tax diversification is not about paying less tax this year. It is about having a choice, every year, about where your income comes from — and that choice is worth real money over a retirement.
The window most people miss
The years between retiring and the start of required minimum distributions are often the lowest-income years of someone’s life. Wages have stopped, but forced withdrawals have not begun. For many people this is the best window they will ever get to convert some traditional money to Roth — paying tax now, at a low rate, to move money into the tax-free bucket and shrink those future forced withdrawals.
Done well, a series of modest conversions across several low-income years can meaningfully lower the tax paid over a lifetime. Done carelessly, a conversion can spill into a higher bracket or bump a Medicare premium. The difference is entirely in the planning.
What this looks like in practice
We are not suggesting you stop using your 401(k) — the upfront deduction is valuable, especially in your peak earning years. The point is to be deliberate: to add Roth contributions where they fit, to keep some money in a plain taxable account for flexibility, and to use those low-income years intentionally. And because none of this is tax advice specific to you, we do it alongside your CPA, so the strategy and the tax return always agree.
