What if my tax rate is the same now and at retirement?

Then both accounts come out to exactly the same after-tax balance — that's the textbook result when the tax rate never changes. Traditional vs. Roth only meaningfully diverges when you expect your tax rate to be different in retirement than it is today.

Should I pick whichever this calculator says comes out ahead?

This shows the pure math outcome under the tax-rate assumptions you enter, but your actual future tax rate is unknowable, and other factors matter too (required minimum distributions, estate planning, tax diversification). This is informational only, not tax or financial advice — many savers reasonably hold both account types.

401(k) vs Roth IRA Calculator

Pre-tax now, or tax-free later? Compare both account types at the exact same cost to your paycheck today, and see which one wins after tax at retirement.

Your Numbers

Enter the pre-tax contribution amount — the same paycheck cost today either way.

Monthly Contribution (pre-tax)Years Until WithdrawalExpected Return (%/yr)Current Tax Rate (%)Retirement Tax Rate (%)

After-tax balance at withdrawal

Traditional 401(k)/IRA

344,280

Grows to 405,036 pre-tax, taxed at 15% on withdrawal

Roth IRA

315,928

Contributing 390/mo after-tax (same paycheck cost), tax-free on withdrawal

At these rates, the Traditional 401(k)/IRA comes out ahead by 28,353 after tax, for the same cost out of your paycheck today.

This compares the same take-home-pay cost today, not the same nominal contribution — the Roth side contributes the after-tax-equivalent amount. Your actual future tax rate is unknowable; both rates here are assumptions you choose. For informational purposes only, not tax or financial advice.

For educational and informational purposes only — not financial, investment, trading, legal or tax advice. See our full Financial Disclaimer.

Why “same contribution amount” isn't a fair comparison

A Traditional 401(k) or IRA contribution comes out of your paycheck before income tax is applied — it lowers your taxable income this year, and the whole balance (your contributions plus all its growth) is taxed as ordinary income when you eventually withdraw it. A Roth IRA works the opposite way: you contribute money that's already been taxed, so there's no deduction today, but qualifying withdrawals in retirement — contributions and growth alike — are completely tax-free.

Because of that, putting the same nominal dollar amount into each one isn't actually an apples-to-apples comparison: a $500 Traditional contribution costs you less out of your take-home pay today than a $500 Roth contribution does, since the Traditional amount hasn't been taxed yet. This calculator fixes that by holding the real cost to your paycheck constant — whatever you enter is treated as the Traditional (pre-tax) contribution, and the Roth side automatically uses the smaller after-tax amount that costs you the exact same amount today.

From there, both balances grow with the same month-by-month compounding at your chosen return rate. The Traditional balance is taxed at your entered retirement tax rate when withdrawn; the Roth balance isn't taxed at all. When your tax rate is expected to be lower in retirement than it is today, Traditional tends to win; when it's expected to be the same or higher, Roth tends to pull ahead — and when the rate never changes at all, the two options are mathematically identical.

Formula used:

Traditional net = [compound growth of pre-tax contribution] × (1 − Retirement Tax Rate)

Roth net = compound growth of [contribution × (1 − Current Tax Rate)] (untaxed)

Key terms:

Same-cost comparison: both sides cost the same amount out of your paycheck today
Tax-rate assumption: your real future tax rate is unknowable; both rates here are chosen by you

Quick answer

A 401(k)/Traditional vs. Roth IRA calculator compares the two account types at the same paycheck cost today: the Traditional side grows a pre-tax contribution and taxes it on withdrawal at your retirement tax rate, while the Roth side grows the smaller after-tax-equivalent contribution and withdraws it tax-free — the two are mathematically identical when your tax rate never changes, and diverge based on whether your retirement tax rate is expected to be lower or higher than today's.

401(k) vs Roth IRA — Guide & FAQs

Why same-cost comparison matters, and what this isn't.

A Traditional contribution is pre-tax — it reduces taxable income today. A Roth contribution is after-tax — it costs the full amount out of take-home pay. Comparing the same NOMINAL dollar amount into both quietly assumes the saver can afford to put in more pre-tax than after-tax, which isn't a fair comparison. This tool instead holds the actual paycheck cost constant: the Roth side contributes whatever after-tax amount equals the same take-home-pay hit as the Traditional contribution.