What Is a Roth 401(k) and Should You Use One?

Most people know what a 401(k) is — but fewer realize there are actually two versions of it. The traditional 401(k) has been around since the 1980s. The Roth 401(k) is the newer version, introduced in 2006. Both live inside your employer's retirement plan, but they work very differently when it comes to taxes.

Understanding the difference could save you tens of thousands of dollars in taxes over your lifetime. Here's everything you need to know.

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How a Traditional 401(k) Works

The traditional 401(k) is the version most people are familiar with. When you contribute money to a traditional 401(k), you contribute pre-tax dollars — meaning that money comes out of your paycheck before federal income taxes are applied.

Here's what that means in practice: if you earn $60,000 a year and contribute $6,000 to a traditional 401(k), the IRS only taxes you on $54,000 of income that year. That's a real, immediate tax break.

Inside the account, your investments grow tax-deferred. You don't owe taxes on dividends, capital gains, or investment growth year after year. The account quietly compounds.

The catch comes in retirement. When you start withdrawing money (after age 59½), every dollar you take out is taxed as ordinary income — at whatever tax rate you're paying at that point in your life. If you're in a high tax bracket in retirement, that could mean a bigger tax bill than you'd expect.

Traditional 401(k)s also have required minimum distributions (RMDs) starting at age 73. The IRS requires you to start withdrawing money whether you need it or not.

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How a Roth 401(k) Works

The Roth 401(k) flips the tax equation. You contribute post-tax dollars — money that's already been taxed as part of your regular income. There's no upfront tax deduction.

But here's the powerful part: the money grows completely tax-free, and qualified withdrawals in retirement are also 100% tax-free. That means every dollar of growth in a Roth 401(k) — potentially decades of compound interest — will never be taxed again.

In 2023, Congress also eliminated the RMD requirement for Roth 401(k)s (beginning in 2024). That means you can let the money grow indefinitely if you don't need it, passing more wealth tax-free to heirs.

The contribution limits for both types are identical. In 2024, you can contribute up to $23,000 per year ($30,500 if you're 50 or older).

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The 5 Key Differences

1. When you pay taxes Traditional: pay taxes in retirement when you withdraw. Roth: pay taxes now, withdrawals are tax-free.

2. Income limits Traditional 401(k): no income limit to contribute. Roth 401(k): also no income limit (this differs from the Roth IRA, which has income limits). Anyone can contribute to a Roth 401(k) through their employer plan regardless of how much they earn.

3. Required Minimum Distributions Traditional: mandatory withdrawals starting at age 73. Roth 401(k): no RMDs starting in 2024, giving you more flexibility to let the account grow.

4. Employer match Your employer's matching contributions always go into the traditional (pre-tax) bucket, even if you're contributing to the Roth side. You'll owe taxes on those employer contributions when you withdraw them in retirement.

5. Flexibility Roth 401(k) contributions (not earnings) can be withdrawn penalty-free under certain conditions. Roth accounts also tend to provide more estate planning flexibility since heirs receive distributions tax-free.

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Who Should Choose a Roth 401(k)?

The classic advice: choose Roth if you expect to be in a higher tax bracket in retirement than you are now. Choose traditional if you expect to be in a lower bracket.

In practice, this often means:

Young workers and early-career earners are usually the best candidates for Roth. If you're in your 20s or early 30s, you're likely at or near the bottom of your lifetime earnings curve. Paying taxes now at a lower rate and locking in decades of tax-free growth is typically a significant win.

High earners who expect taxes to rise also benefit. If you believe marginal tax rates will increase over the next 20–30 years — whether from policy changes or personal income growth — paying today's rates can be advantageous.

People with no other tax-free income sources in retirement. If all your retirement income will be taxed (Social Security, traditional 401(k), pension), having a Roth 401(k) to draw from tax-free gives you flexibility to manage your tax bracket in retirement.

Traditional 401(k)s tend to make more sense for high earners in peak earning years who need the immediate tax deduction to manage a large current tax bill, and who expect lower income (and lower tax rates) in retirement.

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How to Make the Switch or Split Contributions

If your employer offers both options, you don't have to pick one exclusively. Many financial planners recommend splitting contributions — putting some in traditional and some in Roth. This gives you tax diversification: flexibility in retirement to draw from whichever bucket is more advantageous based on your tax situation at that time.

To switch or start using a Roth 401(k):

1. Log in to your employer's 401(k) portal (Fidelity, Vanguard, Empower, etc.)
2. Look for contribution type settings — you'll usually see "Pre-Tax" and "Roth" or "After-Tax Roth" options
3. Update your contribution split. For example: 50% pre-tax, 50% Roth
4. Contributions going forward will be split accordingly

Existing balances don't automatically convert. If you want to move old traditional 401(k) funds to a Roth account, you'd do a Roth conversion — which is a taxable event and a separate decision.

The Roth 401(k) is one of the most powerful tax tools available through your employer. If you're on the fence, a tax diversification split is often the most flexible starting point.