Roth vs Traditional 401(k): A Side-by-Side Breakdown

Maxing your 401(k) in pre-tax dollars is usually the worse deal. Not always — but for more workers than the conventional advice admits. The Roth-versus-traditional decision turns on a single comparison: your current marginal tax rate against your future withdrawal rate. When future rates are higher (or simply unknown), Roth wins.

This article runs the math at three income levels using 2026 brackets, identifies the break-even tax rate, and flags the situations where the standard “save in pre-tax now, pay tax later” advice quietly underperforms.

What’s actually different

Both account types let you contribute up to the 2026 limit of $24,500. The difference is when you pay tax on the money:

A $24,500 traditional contribution costs $24,500 pre-tax — but only ~$18,375 in after-tax dollars at the 25% marginal rate. A $24,500 Roth contribution costs $24,500 in after-tax dollars (you pay tax on the wages first). So the equivalent contribution comparison is between $24,500 traditional and $18,375 Roth — not $24,500 versus $24,500.

This equivalence trips up most quick comparisons. Run the comparison at equal gross contribution and Roth always loses. Run it at equal after-tax cost and the comparison flips.

The break-even formula

The clean way to compare:

Traditional wins if: future tax rate < current tax rate
Roth wins if: future tax rate > current tax rate
Tie at: future tax rate = current tax rate

That’s the math. Everything else — RMDs, Social Security taxation, state taxes, expected returns — adjusts the rates being compared.

Working numbers at three income levels

All scenarios assume 30 years to retirement, 7% annual return, $24,500 contributed annually, and no change in tax law. Federal-only — state tax adds a layer not modeled here.

Scenario A: Single filer, $80,000 income, 22% bracket

Marginal bracket today (2026 single, 22% range): 22%.

• Traditional: $24,500 × 30 years at 7% growth = roughly $2.4M pre-tax. Taxed at retirement bracket on withdrawal.
• Roth equivalent contribution (at 22% marginal): $19,110 after-tax × 30 years at 7% = roughly $1.87M tax-free.
• Break-even: traditional matches Roth when retirement bracket equals 22%.

If retirement bracket is 12%, traditional wins. After tax: $2.4M × 0.88 = ~$2.11M. Beats Roth’s $1.87M by ~$240K.

If retirement bracket is 24%, Roth wins. After-tax traditional: $2.4M × 0.76 = ~$1.83M. Roth’s $1.87M wins by ~$48K.

Scenario B: Married couple, $200,000 income, 22% bracket

Marginal bracket today (2026 MFJ, 22% range): 22%.

Same math as Scenario A — break-even is 22%. The variable is what their retirement bracket looks like. With $1.5M+ in tax-deferred accounts at retirement, RMDs alone often push withdrawals into the 22% or 24% bracket.

For two-earner households with $1M+ projected at retirement, Roth often wins because RMDs force withdrawals at a rate the household can’t fully control.

Scenario C: High earner, $350,000 income, 32% bracket

Marginal bracket today (2026 MFJ, upper portion): 32%.

This is where the conventional wisdom usually wins. The break-even is 32%. To beat traditional, the retiree’s marginal rate must exceed 32% — possible but unusual. Most high earners drop to the 22-24% bracket once W-2 income stops, even with a sizable RMD.

Traditional usually wins for high earners. The exception: those expecting significant Roth conversion ladders, large pension income, or planning to leave the account to heirs (who pay tax at their rate, often higher than the original owner’s retirement rate).

When Roth wins outside the bracket comparison

Five conditions tilt the comparison toward Roth even when current bracket equals projected retirement bracket:

1. You’re early in your career. Your bracket today is lower than your bracket five or ten years from now. Lock in the low rate.

2. You’re saving aggressively for early retirement. Pre-72(t) age, you’ll need a Roth basis to withdraw without penalty. The contribution side of a Roth (not earnings) can be withdrawn at any age, no tax, no penalty.

3. You expect to leave the account to heirs. Inherited Roth IRAs are still tax-free under the 10-year rule. Inherited traditional IRAs are taxed at the heir’s bracket — often higher than yours in retirement.

4. You’re concerned about future tax rates. The federal deficit, demographic pressures, and the 2025-onward expiration of certain TCJA provisions create real upside risk on future brackets. Roth is a hedge.

5. You expect substantial Social Security and pension income in retirement. Both are partially taxable. Adding traditional 401(k) withdrawals on top can push the combined household into a higher effective bracket than expected.

The hidden cost of traditional: provisional income

Social Security taxation depends on provisional income — your AGI plus tax-exempt interest plus 50% of Social Security benefits. Above thresholds ($25,000 single, $32,000 joint), up to 85% of SS benefits become taxable.

Traditional 401(k) withdrawals count toward provisional income. Roth withdrawals do not.

For retirees with $40,000 in Social Security and $40,000 in 401(k) withdrawals, switching the 401(k) source from traditional to Roth can move SS taxation meaningfully:

• $40K SS + $40K traditional withdrawal = ~$60K AGI, 85% of SS taxed = ~$73K total taxable
• $40K SS + $40K Roth withdrawal = $20K provisional income (under threshold), 0% SS taxed = $40K total taxable

That’s a ~$33K swing in taxable income on the same gross retirement income. Worth roughly $7,260/year in federal tax at the 22% bracket — and over a 30-year retirement, more than $200K in cumulative savings.

When traditional wins

Three conditions where traditional 401(k) consistently wins:

1. Current marginal bracket of 32%, 35%, or 37%. Future bracket is unlikely to match. Take the deduction now; pay later at a lower rate.
2. Plan to retire in a low-tax state (no income tax, or much lower than your current state). Defer to the lower-rate jurisdiction.
3. You’ll do strategic Roth conversions in early retirement. A traditional balance is easier to convert at a controlled pace during the low-income years between retirement and Social Security claiming. The Roth conversion calculator can model this.

What most people should actually do

The decision is rarely all-or-nothing. Splitting contributions captures the benefits of both:

• Contribute enough to get the employer match in pre-tax (the match itself is always pre-tax)
• Allocate the rest based on bracket logic — Roth-leaning if under 24%, traditional-leaning if 32%+
• Reassess every 5 years or after major income changes

For a worker in the 22% bracket who can’t decide: a 50/50 split hedges both directions. If future rates rise, the Roth side wins. If they fall, the traditional side wins. Either way, half the contribution lands on the right side.

To project the break-even point with your specific numbers, the 401(k) calculator handles either pre-tax or post-tax projection. Plug in both scenarios and compare the after-tax retirement balance — that’s the only number that matters.

For a refresher on the contribution caps that apply across both sides, see the 2026 401(k) contribution limits.

Pick a side per dollar, not per account. The mix can change every year — what shouldn’t change is making the comparison at all.