What is a Roth 401(k)? High limits, no income cap, tax-free later

A Roth 401(k) is the Roth version of your workplace retirement plan: you contribute money you've already paid tax on, it grows tax-free, and qualified withdrawals in retirement are entirely tax-free. It sits inside your employer's 401(k), so it carries the plan's high contribution limits and gets the employer match — but with Roth tax treatment instead of the traditional pre-tax deal. For a lot of savers, especially earlier in their careers or those who earn too much for a Roth IRA, it's one of the most powerful accounts available, and it's increasingly a checkbox your plan already offers.

How it differs from a traditional 401(k)

Same account, opposite tax timing. A traditional 401(k) contribution is pre-tax — it lowers your taxable income now, and you pay tax on withdrawals in retirement. A Roth 401(k) contribution is after-tax — no deduction today, but the money and all its growth come out tax-free later. The contribution limits are the same and shared: the annual employee limit applies across your traditional and Roth 401(k) contributions combined, not to each separately. Which to choose comes down to the familiar question of whether your tax rate is lower now or later.

The match and the RMD rules

• The employer match historically landed in the pre-tax (traditional) side even if you contributed to the Roth side — so a full-Roth contributor still built some traditional balance. Recent rules let plans offer Roth matching, but it's optional and may be taxable to you in the year received; check how your plan handles it.
• No lifetime RMDs: as of recent law, Roth 401(k)s no longer force required minimum distributions on the original owner — matching the Roth IRA and removing an old reason to roll a Roth 401(k) out at retirement.
• You can contribute to a Roth 401(k) and a Roth IRA in the same year (income permitting for the IRA) — they stack.
• Qualified tax-free withdrawals require being 59½ and having had a Roth account for five years; a Roth 401(k) has its own five-year clock that doesn't transfer to a Roth IRA on rollover.

When to choose it (and when not to)

Lean Roth 401(k) when your current tax rate is relatively low — early career, a temporarily low-income year, or simply a belief that rates (yours or the country's) head higher. Lean traditional when you're in your peak-earning years and expect a lower rate in retirement, since the upfront deduction is worth more. Many people split contributions across both for tax diversification — a mix of taxable-later and tax-free money gives you levers to manage brackets, Medicare surcharges, and Social Security taxation decades from now. And regardless of which side you choose, capturing the full employer match comes first.

The bottom line

A Roth 401(k) marries a 401(k)'s high limits and employer match to a Roth's tax-free withdrawals, with no income limit to lock high earners out. Choose it when your tax rate is relatively low, favor traditional in peak-earning years, and consider splitting for tax diversification — always after securing the match. Know that Roth 401(k)s no longer carry lifetime RMDs, that matching dollars may be handled differently than your own, and that the account's five-year clock is its own. If your plan offers the Roth option and it fits your bracket, it's one of the best retirement tools you have access to.