Roth vs traditional: a decision framework

The one question that decides it

Strip away the jargon and Roth-vs-traditional is a single question: is your marginal tax rate higher now, or will it be higher when you withdraw?

• Traditional (pre-tax): you skip tax at today's marginal rate and pay tax at withdrawal, at whatever rates exist then.
• Roth (after-tax): you pay tax at today's rate and withdraw tax-free later, provided the rules are met.

If the rate is the same in both periods, the math is a wash — a counterintuitive fact worth sitting with. $10,000 pre-tax growing 3× then taxed at 25% leaves $22,500; $7,500 after-tax (the same $10,000 taxed at 25% first) growing 3× leaves $22,500. Identical. The difference in rates, now versus later, is the whole game.

What nobody can promise you

Here's the honest part most articles skip: the comparison requires predicting your future tax rate, and nobody can do that with certainty. It depends on your future income, future tax law written by future Congresses, which state you'll live in, and how large your pre-tax balances grow. Every recommendation in this space is a judgment about probabilities, not a fact. What you can do is reason carefully about your own situation — and hedge where the answer is unclear.

When the reasoning tends to favour Roth

• Early career, income likely to rise. Paying tax in the 12% or 22% bracket now, to avoid a plausibly higher bracket later, is the classic Roth case.
• You expect a pension. A CalPERS or CalSTRS pension is taxable income that fills your lower brackets in retirement before your first savings withdrawal — pension households often face higher retirement marginal rates than they expect, which strengthens Roth.
• You value optionality. Roth IRAs have no required minimum distributions during the owner's lifetime, Roth IRA contributions (not earnings) can be withdrawn anytime without tax or penalty, and tax-free accounts are generally friendlier to heirs.
• A temporarily low-income year. A sabbatical, a business loss, early retirement before Social Security — low-bracket years are the natural moments for Roth contributions or conversions.

When the reasoning tends to favour traditional

• Peak earning years. If you're in a high bracket now and expect ordinary retirement spending, the deduction today is worth more than tax-free treatment later — you'll likely withdraw across lower brackets than the one you're deducting against.
• You plan to retire in a lower-tax situation. Retirement income lower than working income is the norm, and withdrawals fill the brackets from the bottom up: some of every withdrawal comes out at the lowest rates.
• The deduction enables more saving. If the tax savings from a traditional contribution is what lets you afford a larger contribution, that practical effect can outweigh theoretical rate comparisons.

Splitting the difference is a legitimate strategy

Because the future rate is unknowable, holding both pre-tax and Roth money — "tax diversification" — is not indecision; it's hedging. In retirement, a mix lets you fill low brackets with traditional withdrawals and take anything above that from the Roth, managing your tax bill year by year instead of accepting whatever one account type dictates. Many savers land on the match and core deferrals traditional, plus a Roth IRA on the side — not because it's provably optimal, but because it's robust to being wrong.

The backdoor Roth — and the pro-rata trap

Direct Roth IRA contributions phase out at higher incomes (the IRS sets the thresholds annually). The widely used workaround — contribute to a non-deductible traditional IRA, then convert it to Roth — is commonly called a backdoor Roth. The two-step itself is well established. The trap is the pro-rata rule (IRC §408(d), reported on IRS Form 8606): a conversion is taxed based on the ratio of pre-tax to after-tax money across all your traditional, SEP and SIMPLE IRAs combined, not just the account you convert from.

Concretely: if you hold a $93,000 pre-tax rollover IRA and convert a fresh $7,000 non-deductible contribution, 93% of that conversion is taxable — not 0%, as people expect. This is also why rolling an old 401(k) into an IRA can quietly wreck a future backdoor strategy; it's mistake #4 in our rollover mistakes guide. If a backdoor Roth is on your radar, look at your IRA balances before any rollover, and consider whether pre-tax IRA money could move into a current employer plan first. This is squarely a talk-to-your-CPA topic.

The RMD difference

Traditional 401(k)s and IRAs carry required minimum distributions — currently beginning at age 73 under SECURE 2.0, scheduled to rise to 75 in 2033 (IRS.gov, Retirement Topics: RMDs). Roth IRAs have no lifetime RMDs, and since 2024 Roth 401(k) accounts are exempt as well. For savers who may not need the money on the government's schedule, this is a quiet but real point for Roth: it preserves control over the timing of taxable income late in life.

Common questions