Roth vs Traditional 401(k) Calculator
Compare Roth and traditional 401(k) contributions at the same take-home cost, including contribution caps and reinvested surplus. Free, with no signup.
Reviewed October 25, 2026
Short answer
Before contribution caps bind, equal current and retirement tax rates produce equal after-tax results when tax savings are reinvested. At the defaults, both strategies reach about $330,660 after 20 years.
Free to use. No signup. Results update as you edit.
Both use $10,000 of annual take-home pay. Annual 401(k) deposits: Roth $10,000; traditional $13,333.
Tax savings first fund a larger traditional contribution. Once the $24,500 cap binds, all remaining budget is invested in a taxable side account: Roth $0/year; traditional $0/year. No tax savings are assumed spent.
Retirement tax-rate sensitivity
Scroll horizontally on small screens.
| Withdrawal tax rate | Roth total | Traditional total |
|---|---|---|
| 15% | $330,660 | $374,747 |
| 25% | $330,660 | $330,660 |
| 35% | $330,660 | $286,572 |
2026 regular employee limit of $24,500; no catch-up contributions. This isolates tax treatment with constant rates, zero inflation, and qualified Roth withdrawals. It is not a tax-bracket or Roth conversion calculator.
This is an educational estimate, not tax or financial advice. Figures reflect the law year shown and the inputs you provide. Consult a qualified professional before acting.
Sources
- 2026 retirement plan contribution and compensation limits — Internal Revenue Service
2026 regular employee limit of $24,500, $72,000 combined additions limit, and $360,000 compensation cap. Catch-up contributions are outside these tools.
Accessed October 25, 2026
- Roth comparison chart — Internal Revenue Service
Pre-tax vs after-tax contributions, shared employee limits, and qualified Roth withdrawal treatment. Older annual limits on the chart are superseded by the 2026 limits cited separately.
Accessed October 25, 2026
How it’s calculated
- Use the same annual reduction in take-home pay in both strategies. The uncapped traditional contribution is budget ÷ (1 − current income-tax rate). Roth contributions use the budget directly.
- Cap each alternative separately at $24,500 or eligible pay, whichever is lower. These are alternative scenarios, not two separate limits you can use simultaneously.
- Invest every remaining dollar of take-home budget in a taxable side account. Make all deposits at year end and apply the same constant annual return.
- At the end, tax all traditional assets at the selected withdrawal rate. Qualified Roth withdrawals are tax-free. Tax only the side account's positive gains at the chosen gains rate, with no annual tax drag. Repeat at withdrawal rates ten percentage points above and below the selected rate.
Worked equal-cost 401(k) example
- Take-home budget / pay
- $10,000 / $100,000 a year
- Current / retirement tax rate
- 25% / 25%
- Return / years
- 5% / 20
- Side-account gains tax
- 15% (no side deposits at these inputs)
Result
Roth and traditional each end at about $330,660 after tax.
Roth deposits $10,000 a year. Traditional deposits $13,333.33 before tax at the same $10,000 take-home cost, then retains 75% at withdrawal. Both equal $10,000 × (1.05^20 − 1) ÷ 0.05 after tax.
What this calculator does not cover
- No catch-up contributions, mandatory Roth catch-up, employer match, payroll taxes, changing marginal brackets, credits, early-withdrawal penalties or RMDs.
- The $24,500 cap and pay stay constant. Inflation is assumed zero, so nominal and base-year dollars coincide; future law changes are not projected.
- Side-account gains are taxed only at final liquidation. Dividends, annual realized gains, tax-loss harvesting and differing investment returns are not modeled.
- The retirement tax rate is the rate on modeled withdrawals, not necessarily your household's headline marginal bracket. Roth distributions must satisfy qualified-distribution rules.
Frequently asked
- Are the traditional tax savings spent or reinvested?
- Reinvested in full. They first allow a larger pre-tax 401(k) contribution; after the cap binds, the remaining take-home budget goes to the taxable side account. Spending the savings would be a different-cost comparison.
- Can I contribute $24,500 to each type?
- No. Roth and traditional employee deferrals share one limit. This tool compares all-Roth and all-traditional alternatives; it does not add their limits.
Related reading
Explore more worked examples on the retirement planning blog.