Short answer: a traditional 401(k) lowers your taxable income now and taxes withdrawals in retirement, while a Roth 401(k) is funded with after-tax dollars and qualified withdrawals come out completely tax-free. If you expect your tax rate to be lower in retirement, traditional usually wins; if you expect it to be higher — or you are early in your career in a low bracket — Roth usually wins. When you are unsure, splitting your contributions between the two is a sensible hedge.
The one difference that matters
Traditional contributions go in pre-tax, grow tax-deferred, and are taxed as ordinary income when you withdraw them. Roth contributions go in after tax, grow tax-free, and come out tax-free in retirement — provided the withdrawal is qualified, meaning you are at least 59½ and your first Roth contribution to the plan was at least five years earlier.
Everything else is shared. Both sit inside your employer’s plan, both are subject to the same annual contribution limit, and both let you invest the same way. Neither changes what you pay in Social Security and Medicare taxes.
The 2026 limits, shared by both
For 2026, the IRS set the employee elective deferral limit at $24,500 (up from $23,500 in 2025), under IRS Notice 2025-67. That cap covers traditional and Roth contributions combined — you cannot put $24,500 in each. Workers age 50 or older can add an $8,000 catch-up, for a total of $32,500, and workers ages 60 to 63 get a larger “super catch-up” of $11,250, for a total of $35,750. The overall limit from all sources, including employer contributions, is $72,000 for 2026.
One more rule that surprises people: the $24,500 cap follows you, not your plan. If you change jobs mid-year and contribute to two different 401(k)s, the combined total still cannot exceed $24,500. And unlike a Roth IRA, a Roth 401(k) has no income limit — even very high earners can contribute the full amount, as long as their plan offers a Roth option.
The worked example: when the rates are equal, it is a tie
Suppose you have $10,000 of gross pay to save, your federal tax rate is 22%, and the money triples by retirement. The two paths come out identical:
| Traditional | Roth | |
|---|---|---|
| Amount invested | $10,000 (pre-tax) | $7,800 (after 22% tax) |
| Value at retirement (3x) | $30,000 | $23,400 |
| Tax on withdrawal | $6,600 (22% of $30,000) | $0 |
| You keep | $23,400 | $23,400 |
That is the key insight: if your tax rate is the same now and in retirement, the choice does not matter. The entire decision is a bet on which rate will be higher.
Run your own version of this math with our compound interest calculator to see how the numbers scale over a full career.
When traditional wins
Traditional is usually the better pick when you are in your peak earning years. If you are in the 32% or 35% bracket now and expect to retire into the 22% bracket, every pre-tax dollar saves you 32 or 35 cents today and costs only 22 cents later. The deduction also lowers your adjusted gross income, which can affect eligibility for other tax breaks.
When Roth wins
Roth is usually the better pick when you are young or in a low bracket. A worker in the 12% bracket pays just $1,200 of tax on a $10,000 contribution and never pays tax on that money again — including decades of growth. The same logic applies to anyone expecting a much higher income later in their career: pay the low rate now, lock it in.
The employer match and the 2026 high-earner rule
Two details that trip people up. First, the employer match: matching dollars almost always land in the pre-tax bucket, even when your own contributions are 100% Roth. (SECURE 2.0 lets plans offer a Roth match, but it is still rare.) That means a Roth-only saver still ends up with some taxable money in retirement.
Second, starting in 2026, a SECURE 2.0 rule takes effect for high earners: if your wages from your current employer exceeded $150,000 in the prior year, any catch-up contributions you make must go into the Roth side. You cannot take a pre-tax deduction on catch-up dollars. If that applies to you, check that your plan offers a Roth option — without one, you cannot make catch-up contributions at all.
The practical answer: split when you are unsure
Nobody can forecast their retirement tax bracket precisely — tax law, income, and life all change over 30 years. A common approach in peak-earning years is a majority-traditional split with a meaningful Roth slice, adjusted whenever income changes. A low-income year is a good time to tilt toward Roth; a high-income year is a good time to tilt toward traditional. If you are choosing between account types more broadly, read our guide on 401(k) vs IRA: which retirement account first.
Frequently asked questions
Can I contribute to both a Roth and a traditional 401(k) in the same year?
Yes. You can split your contributions between the two in any proportion, as long as the combined total does not exceed the annual IRS limit — $24,500 for 2026, or $32,500 if you are age 50 or older. Your plan tracks the two buckets separately so each keeps its own tax treatment.
Does a Roth 401(k) have required minimum distributions?
No, not during the owner’s lifetime. Since 2024, the SECURE 2.0 Act eliminated lifetime RMDs for designated Roth accounts in employer plans, matching the long-standing Roth IRA rule. Traditional 401(k) balances still require distributions starting at age 73, or 75 if you were born in 1960 or later.
Does contributing to a Roth 401(k) lower my taxable income?
No. Roth contributions are made with after-tax dollars, so they do not reduce your current year’s taxable income the way traditional pre-tax contributions do. That is the tradeoff: you give up the deduction now in exchange for tax-free qualified withdrawals in retirement, including all investment earnings.
Is a Roth 401(k) better than a Roth IRA?
They are different tools, not rivals. A Roth 401(k) has no income limit and a much higher contribution ceiling ($24,500 versus $7,500 for an IRA in 2026), plus the employer match. A Roth IRA offers far more investment choices and lets you withdraw contributions — not earnings — at any time without tax or penalty.