Traditional 401(k) vs Roth 401(k)
Last updated August 2026
Short answer
At identical tax rates in both periods the two are arithmetically the same. Everything that makes the decision interesting comes from the rates not being identical.
The core arithmetic
$1,000 pre-tax growing tenfold becomes $10,000, taxed at 22% on withdrawal, leaving $7,800.
$780 after tax at the same 22% growing tenfold becomes $7,800, withdrawn tax-free.
Identical. The difference appears only when the rate at contribution differs from the rate at withdrawal.
What tilts it toward Roth
Being early in a career, when your rate is likely lower than it will be later.
Expecting large traditional balances that will force sizeable required distributions at 73, pushing you into a higher bracket then.
Wanting tax diversification, so that some retirement income can be drawn without adding to taxable income at all.
What tilts it toward traditional
A high current marginal rate, where the deduction is worth a great deal today.
Expecting a lower rate in retirement, which is the ordinary case for someone at peak earnings.
Living in a high-tax state now and planning to retire somewhere with no income tax.
Try it in Walnut
Walnut connects to brokerage accounts and analyses what you hold, so a mixed pre-tax and Roth balance can be read as one portfolio.
The maxing-out asymmetry
At the limit, a Roth contribution shelters more real money, because the tax has already been paid on it.
$24,500 of Roth is worth more in retirement than $24,500 of traditional, which carries a future tax liability inside it.
For anyone contributing the maximum, that asymmetry is a genuine argument for Roth that the simple arithmetic above does not capture.
Splitting, and changing your mind
Most plans allow contributions to be divided between the two in any proportion, and changed during the year.
Splitting hedges the rate uncertainty rather than expressing indecision, and it produces both taxable and tax-free income in retirement.
Past contributions cannot be reclassified. Some plans allow in-plan Roth conversions, which triggers tax in the year of the conversion.
Bracket management in retirement
Traditional balances create taxable income at withdrawal, which interacts with Social Security taxation and Medicare premium surcharges.
Roth withdrawals do not appear in that calculation at all, so holding both allows income to be managed against bracket thresholds.
That flexibility is the practical case for splitting, and it does not depend on guessing future rates correctly.
Sources
The 2026 deferral and catch-up limits are from IRS Notice 2025-67. Designated Roth account rules, including the five-year requirement and the removal of lifetime required distributions, are at FAQs on designated Roth accounts. Walnut is informational and is not an investment adviser. This guide is educational and not personalized tax advice.
FAQ
What is the difference?
+
When the tax is paid. Traditional contributions reduce this year's taxable income and are taxed on withdrawal. Roth contributions are made after tax and qualified withdrawals are entirely tax-free, growth included.
Which should I choose?
+
Compare your tax rate now against what you expect in retirement. A higher rate now favours traditional; a lower rate now, which usually means earlier in a career, favours Roth. Where you genuinely cannot tell, splitting is a reasonable answer.
Where does the employer match go?
+
Historically to the pre-tax side regardless of what you choose. SECURE 2.0 allows plans to offer Roth matching, but it is optional and many have not adopted it, so most Roth 401(k) savers also accumulate a traditional balance.
Which gives more spendable money in retirement?
+
At the same tax rate in both periods, the two are mathematically identical. The difference arises when rates differ, and from the fact that a maxed Roth contribution shelters more real money because the tax has already been paid.
Do required minimum distributions differ?
+
Yes. Traditional balances must start distributing at 73. Designated Roth accounts in workplace plans no longer carry lifetime required distributions after SECURE 2.0, which is a real planning advantage.
What about state taxes?
+
Worth thinking about if you might move. Someone contributing in a high-tax state and retiring to a state with no income tax gets more from the traditional deduction, and the reverse favours Roth.
Can I change my mind later?
+
You can change future contributions at any time in most plans. Past contributions cannot be reclassified, though some plans permit in-plan Roth conversions, which is a taxable event in the year it happens.
Does the choice affect anything besides income tax?
+
Yes. Traditional withdrawals count as income in retirement, which affects how much of your Social Security is taxable and whether Medicare premium surcharges apply. Roth withdrawals do not enter those calculations at all.
Can I convert my traditional balance to Roth later?
+
Some plans permit in-plan Roth conversions, and a rollover to a Roth IRA is possible after leaving. Either way the converted amount is taxable in the year of conversion, so it is a decision about timing rather than a way to undo the original choice.
Is there a reason to hold both rather than picking one?
+
Yes, and it does not require predicting rates. Holding both lets you choose in retirement which account a withdrawal comes from, which is what makes managing income against bracket thresholds possible at all.
What if my employer only offers one of them?
+
Then the decision is made for you inside the plan, and the other side can be approximated elsewhere. Someone with only a traditional 401(k) can add a Roth IRA if income permits, and someone with only a Roth option can hold pre-tax money in a deductible traditional IRA.