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Roth vs Traditional 401(k) Calculator

Pay the tax now or pay it later? Type your contribution, your tax bracket today and your best guess for retirement, and see which 401(k) leaves more after taxes — plus the crossover chart that shows exactly where the answer flips.

Which 401(k) wins after taxes?

Both paths invest the same pre-tax dollars, so the comparison stays fair: Traditional is taxed at withdrawal, Roth is taxed up front and grows tax-free.

Annual contribution $

Pre-tax dollars — the same amount races on both tracks.

Years to retirement

Expected return %

Your tax rate now %

Your marginal rate — the tax on your last dollar.

Your tax rate in retirement %

Nobody knows this — it is the whole decision.

Guess:

Traditional wins$7,612.26 more after taxesTraditional: $66,987.84 after taxes · Roth: $59,375.59 tax-free

Traditional · after taxes$66,987.84Winner

Roth · tax-free$59,375.59Winner

Traditional after-taxRoth after-taxYour rate today

Traditional$7,612.26

Roth$0

Beam tips toward the richer path · Traditional keeps $7,612.26 more after taxes

Traditional wins: $7,612.26 more after taxes. Paying 12% in retirement beats paying 22% today: the Traditional 401(k) leaves $66,987.84 after taxes versus $59,375.59 tax-free in the Roth — a $7,612.26 gap.

How it works: both tracks invest the same pre-tax dollars and compound at your expected return. The Traditional balance is taxed once, at withdrawal, at your retirement rate. The Roth is taxed once, up front, at your current rate — then it grows and withdraws tax-free. The winner is decided entirely by which rate is lower, and the crossover chart shows exactly where the answer flips.

How the Roth vs traditional math works

The 401(k) choice is really one question asked twice: do you want to pay taxes on this money now, or later? A traditional 401(k) takes the money pre-tax — you skip the tax today and pay it when you withdraw in retirement. A Roth 401(k) flips it: you pay tax on the money now, and it grows and comes out completely tax-free. Growth is identical on both tracks; only the timing of the tax differs.

The formula

Traditional after-tax = contribution × (1 + return)^years × (1 − retirement tax rate) · Roth after-tax = contribution × (1 − current tax rate) × (1 + return)^years

Notice the two formulas are the same multiplication in a different order — tax now then grow, or grow then tax. That is why the honest answer surprises people: if your tax rate is the same on both ends, the two paths leave exactly the same amount. Commutativity is doing the work. The winner is simply whichever end has the lower rate.

Worked example: $10,000 a year for 30 years at 7%

At 7% for 30 years, every dollar grows by a factor of 7.612 — so $10,000 a year becomes $76,122.55 before any tax. Now the timing matters.

Traditional (22% today, 12% in retirement): the full $76,122.55 is taxed at 12% on the way out — $9,134.71 in taxes — leaving $66,987.84.

Roth: the $10,000 is taxed at 22% up front, so $7,800 goes in; it grows to $59,375.59 and not a cent is taxed at withdrawal.

The verdict: Traditional wins by $7,612.26 — purely because 12% is smaller than 22%. Flip the retirement rate to 24% and Roth wins by $1,522.45. Set both rates to 22% and the two balances print the identical $59,375.59.

Where this comes in handy

The bracket-drop check: if you expect meaningfully lower income in retirement — the classic case — Traditional usually wins; run your numbers and watch the crossover chart.
The early-career play: in a low bracket now with raises ahead, Roth locks in today's cheap rate forever.
The hedge: genuinely unsure? Split contributions between both — the Roth vs traditional guide explains why that is the rational default.
The match maximizer: contribute at least enough to capture the full employer match first — the match itself always lands on the pre-tax side.
The tax-law bet: worried Congress raises rates later? Roth is your insurance policy against that.

Educational math, not tax advice — use your marginal rate (the tax on your last dollar, federal plus state), and talk to a tax professional for your situation.

Roth vs traditional 401(k) — frequently asked questions

What is the one rule that decides Roth vs traditional?

Compare your marginal tax rate today with your best guess at your marginal rate in retirement. Lower later → Traditional wins. Higher later → Roth wins. Same on both ends → the math ties exactly, and the tiebreakers (flexibility vs today's deduction) decide. Everything else is commentary.

If my tax rate is the same now and in retirement, does the choice matter?

Mathematically, no — that is the dead-even tie the calculator shows. Paying 22% now then growing, or growing then paying 22%, leaves the identical balance, because multiplication does not care about the order. When it ties, pick Roth for flexibility (no required withdrawals, tax-free access to contributions) or Traditional for the bigger paycheck today via the deduction.

Where does my employer's 401(k) match go — Roth or traditional?

The match always lands on the pre-tax (traditional) side of your account, even if your own contributions are 100% Roth. So choosing Roth does not mean your whole account is tax-free — the employer dollars and their growth will still be taxed at withdrawal.

Can I split my contributions between Roth and traditional?

Yes, if your plan offers both — most do. You can route, say, half of each paycheck to Roth and half to traditional. Splitting is the rational hedge when you genuinely cannot guess your retirement bracket, and it gives you two tax "buckets" to draw from in retirement, which itself is a planning advantage.

Do Roth 401(k)s have required minimum distributions?

No — a 2024 rule change (SECURE 2.0) eliminated required minimum distributions for Roth 401(k)s, matching Roth IRAs. Traditional 401(k)s still force withdrawals starting at age 73, which is one of Roth's genuine tiebreaker advantages: the money can sit and grow as long as you like.

What if I think tax rates will rise in the future?

That tilts the math toward Roth — you are locking in today's rates. But weigh your personal bracket more than the statutory rates: most people land in a lower bracket in retirement because they stop earning a salary, which often swamps a few points of rate changes. Use the "higher than now" preset to see how big the rate jump would need to be.

Is a Roth 401(k) the same thing as a Roth IRA?

Same tax treatment, different accounts. The Roth 401(k) lives inside your employer's plan — no income limit on choosing it, and much higher contribution limits. The Roth IRA is yours alone, with income phase-outs on eligibility and lower limits. Many people fund both: the 401(k) for volume, the IRA for investment choice.

Can I switch from traditional to Roth in the middle of the year?

Usually yes — most plans let you change your contribution type (and amount) at any time through your benefits portal. The switch only affects future paychecks; money already contributed keeps its original tax character.