Free roth 401(k) vs traditional 401(k) calculator
See which 401(k) election leaves more after tax, given your tax rate now versus in retirement — updated live, as you type.
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Estimates only, based on a constant real return and steady saving. Not financial advice.
Results are estimates. Consult a professional.
Roth 401(k) vs Traditional 401(k): what the calculator decides
The Roth 401(k) vs Traditional 401(k) calculator answers the one question that decides which to choose: which leaves more money after tax in retirement. Both are workplace plans with the same 2025 contribution limit; the only difference is when you pay income tax. Enter the amount, your tax rate now, your expected tax rate in retirement, a return, and the years until withdrawal, and the tool reports the after-tax balance each option produces and which one wins.
A traditional 401(k) contribution is pre-tax — you skip income tax today and pay it on every dollar you withdraw later. A Roth 401(k) contribution is after-tax — you pay income tax now, and qualified withdrawals come out completely tax-free. There is no universally better choice; the winner is determined entirely by whether your tax rate is higher now or in retirement.
How the after-tax comparison is calculated
The calculator grows the same starting amount for both options and applies tax at the point each plan charges it — withdrawal for traditional, contribution for Roth — then compares the after-tax results.
That symmetry is the key insight. When the two rates match, Roth and traditional produce exactly the same after-tax dollars — the return cancels out. The advantage only appears when the rates differ: pay tax when your rate is lower. A lower rate today than in retirement favours Roth; a lower rate in retirement than today favours traditional.
IRS — Roth comparison and the designated Roth 401(k) account rules.A worked example: higher tax rate now than later
Devin can direct $100,000 (in equivalent pre-tax terms) into either election, expects a 7% return over 20 years, is in the 32% bracket today, and expects a 22% rate in retirement. With today's rate higher, the math should favour the traditional 401(k).
Step 1 — Traditional path
Step 2 — Roth path
Step 3 — Compare
Which election wins, by tax-rate scenario
The table holds $100,000, a 7% return, and 20 years constant, and varies only the tax rates so you can see the rule directly: pay tax in the year your rate is lower.
| Tax rate now | Tax rate in retirement | Traditional after-tax | Roth after-tax | Winner |
|---|---|---|---|---|
| 32% | 22% | $301,835 | $263,139 | Traditional |
| 24% | 22% | $301,835 | $294,096 | Traditional |
| 22% | 22% | $301,835 | $301,835 | Tie |
| 22% | 24% | $294,096 | $301,835 | Roth |
| 22% | 32% | $263,139 | $301,835 | Roth |
$100,000 at 7% over 20 years. Traditional taxes the withdrawal; Roth taxes the contribution. Figures computed by this calculator.
Reasons to choose Roth even on a tie
- You expect higher taxes later — either from rising income or the chance of higher future tax rates. Locking in today's rate with Roth hedges that.
- Early-career, low bracket. A young saver in the 12–22% range often never pays a lower rate again — strong Roth territory.
- No lifetime RMDs. Roth 401(k)s no longer force withdrawals during your lifetime, leaving the balance to grow and pass on tax-free.
- Tax diversification. Holding both lets you manage retirement income across brackets year by year, regardless of where rates land.
- Traditional still wins for high earners now who expect a lower bracket in retirement — the deduction today is worth more than the tax-free growth.
Whichever election you pick, project the balance it builds with the 401(k) calculator, and check the cost of dipping in early with the 401(k) early withdrawal penalty calculator.
Accuracy, assumptions, and sources
This calculator compounds a single amount at a constant return and applies your stated tax rates — at withdrawal for traditional, at contribution for Roth — to compare after-tax outcomes. It assumes one fixed return, flat tax rates rather than graduated brackets, and that you invest the traditional tax saving rather than spending it (otherwise traditional's edge shrinks). It excludes state tax and the time-varying nature of real brackets. It is a planning estimate, not tax advice — confirm your situation with the IRS or a tax professional.
IRS — Designated Roth accounts in a 401(k) or 403(b) plan.IRS — Roth comparison chart (Roth 401(k) vs traditional pre-tax elective deferrals).Frequently asked questions about the free roth 401(k) vs traditional 401(k) calculator
About this Roth 401(k) vs Traditional 401(k) calculator
This calculator decides the Roth-versus-traditional 401(k) question on the only basis that matters: which leaves more money after tax in retirement. It grows the same amount for both elections and applies income tax where each plan charges it — at withdrawal for traditional, at contribution for Roth — then names the winner. The result turns entirely on whether your tax rate is higher now or in retirement.
It belongs to our retirement calculators; see them all on the calculators home. The shared 2025 limits and Roth rules come from the IRS. This is a planning estimate, not tax advice.