Educational content, not personalized advice. Your situation may turn on facts this piece doesn’t address.
Most high-earning households make the pre-tax vs. Roth decision by guessing where tax rates are headed, and the guess is almost always “up.” That points them toward Roth, which feels safe, which ends the analysis.
The decision hinges on something narrower than a rate forecast. What matters is the rate you’d pay to contribute a dollar today compared to the rate you’d pay to withdraw that dollar in retirement.
Pay less tax when you pay tax.
That’s the mantra, which we’re borrowing from Cody Garrett and Sean Mullaney’s Tax Planning to and Through Early Retirement — the clearest technical treatment of this math we’ve come across and worth reading in full.
One household, worked through
Take a dual-career household earning $450,000. Their marginal rate on the last dollar of comp is 32% federal plus roughly 9% state, call it 41% all-in. A full $23,500 pre-tax 401(k) contribution in 2026 deducts about $9,600 in current-year tax. Cash the household doesn’t owe that year.
Now move the same couple to retirement, drawing $180,000 a year — some Social Security, some from the portfolio. After the standard deduction, taxable income is around $150,000, most of it sitting in the 12% and 22% federal brackets. Federal effective rate lands near 15%. Add about 8% effective state tax. All-in effective: ~23%.
The spread: 41% in, 23% out. Eighteen percentage points per dollar, every year, on the full contribution. That’s a structural head start the Roth has to overcome through some other mechanism.
Roth catches up in three scenarios.
First, if your retirement tax rate ends up meaningfully higher than your working rate — possible for some households, uncommon for peak-earning dual-career couples whose working years are their lifetime income peak.
Second, if the pre-tax savings never get invested and get absorbed into cash flow instead. Common enough to matter, and the scenario in which Roth becomes the structurally safer call for behavioral reasons alone.
Third, legacy. A Roth passed to non-spouse heirs under the SECURE Act’s ten-year distribution rule keeps compounding tax-free for the beneficiary’s decade and then exits untaxed, which is a meaningful estate advantage the traditional account doesn’t have. For households who plan to leave significant money behind, that argument for Roth holds without any rate forecasting at all.
What actually moves the answer
Six things.
Do the tax savings actually get invested? Every pre-tax comparison assumes the $9,600 the household didn’t pay in tax lands somewhere productive — a taxable brokerage, an HSA, additional 529 funding, extra mortgage principal. If it gets absorbed into lifestyle, the pre-tax advantage is smaller.
Cash flow today. Roth costs more out of pocket. A $23,500 Roth contribution, for our anchor household, is about $39,800 of gross comp. When a family has daycare, a recent mortgage, and a parent who needs help, that gap is a binding constraint. The best contribution is the one you can keep making.
Future RMD pressure. A $23,500 pre-tax contribution compounding at 7% above inflation for 30 years grows to over $3 million — illustrative only, not a projection or guaranteed return. A two-earner couple doing this for most of a career can easily reach traditional balances well into the mid-seven figures. Required distributions at 73 or 75 stack on top of Social Security and any pension income, pushing the household back into the brackets they tried to avoid on the way in.
Other income filling the lower brackets. A household with a pension, rental income, deferred comp, or a spouse who keeps working part-time has its lower brackets already occupied. Pre-tax withdrawals stack on top and get taxed at a higher marginal rate than the clean anchor-household example above suggests. The more low-bracket income you expect in retirement, the more Roth makes sense during your working years.
The early-retirement Roth conversion window. Between stopping work and the year Social Security and RMDs begin, many households sit in a multi-year low-income window. That’s when Roth conversions happen at favorable rates. Our clients who plan for this window end up converting pre-tax dollars at a rate closer to their future effective rate than their current marginal rate, which is the arbitrage the original contribution decision was trying to capture. Practical consequence: the pre-tax vs. Roth choice is less final than it feels. Some of it gets resolved in the conversion window rather than in the contribution election.
Mega backdoor Roth. Plans that allow after-tax 401(k) contributions with in-plan conversion can push the total annual 401(k) figure toward $70,000. MBDR gives you more tax-advantaged shelf space. Your base pre-tax vs. Roth decision still has to happen on its own merits, and “pre-tax to the employee limit, then MBDR on top” is the shape that decision usually takes once cash flow supports the extra contribution.
Where this gets complicated
State of residence is a bigger variable than most people weight it. A pre-tax decision made in Oregon or California and retired into Florida or Texas looks considerably better on the exit than the original worksheet predicted. The reverse also holds.
Legislation keeps moving. RMD ages have been pushed twice in recent years, bracket schedules have their own sunset clauses, and backdoor and mega backdoor conversions have been periodically threatened by proposed legislation. Legislative uncertainty argues for planning optionality across account types so you aren’t fully exposed to any single rule set staying in place.
Employer plan design is another constraint. Some 401(k) plans don’t offer a Roth option. Some don’t permit after-tax contributions. Some allow after-tax but not in-plan conversion. The best strategy is the one your plan actually supports, and the summary plan description is the right first read before running any numbers.
Backdoor Roth IRA mechanics trip up sophisticated households more than they should. The pro-rata rule treats all your traditional IRAs as one pool for the tax calculation. Any rollover IRA from an old 401(k) has to be addressed — usually rolled back into a current employer plan that accepts it — before a clean backdoor is available.
Back to the mantra
The pre-tax vs. Roth question is about the shape of your full tax picture, current and retirement, and about whether you’ll do the things the math assumes — invest the savings, manage the conversion window, keep the account mix honest over time.
Among the households we work with, the pattern that emerges most often is a weighted default to pre-tax today, some Roth along the way for diversification, and a plan to convert aggressively in the early-retirement window. Whether that pattern fits a given household depends on the specifics, and it assumes a conversion window will exist. For households who plan to work past Social Security age, or who will have deferred comp and pension income filling their early retirement years, the window is narrower or absent, and the Roth mix during working years may need to be proportionally higher.
All of that comes from running your specific numbers and being honest about the adjacencies.
Pay less tax when you pay tax.
Nothing in this essay is investment, legal, or tax advice. It’s a general discussion of concepts I find useful in my work and shouldn’t be relied on as a recommendation for your specific situation. Talk to a qualified advisor (ideally one who knows you) before acting on anything here.
