What’s the Real Difference Between a 401(k) and a Roth IRA?

Direct answer: The core difference is when the money gets taxed, not just which account it sits in. A traditional 401(k) is funded with pre-tax income, and withdrawals in retirement are taxed; a Roth IRA is funded with after-tax income, and qualified withdrawals in retirement are tax-free. Per the IRS’s own 2026 limits, a 401(k) allows contributing up to $24,500 a year (more with catch-up contributions for those 50+), while an IRA, Roth or traditional, caps at $7,500, and Roth IRA eligibility phases out entirely above $168,000 in income for single filers and $252,000 for married couples filing jointly.

The Actual Tax-Timing Difference, Not Just an Account-Type Label

The single most important distinction is when a dollar gets taxed, not just what the account is called. Money going into a traditional 401(k) reduces taxable income the year it’s contributed, then gets taxed as ordinary income when it’s withdrawn in retirement. Money going into a Roth IRA has already been taxed as regular income before it’s contributed, so qualified withdrawals in retirement, including all the growth the account earned over the years, come out completely tax-free. Neither is universally better, it depends on whether a household expects to be in a higher or lower tax bracket in retirement than they are now, a real, individual judgment call, not a fixed rule.

The Real 2026 Contribution Limits

Per the IRS’s own 2026 figures, a 401(k) (along with 403(b) and most 457 plans) allows contributing up to $24,500 a year, with an additional $8,000 catch-up contribution allowed for those age 50 and older, and a special $11,250 catch-up for ages 60 through 63. An IRA, whether traditional or Roth, caps significantly lower: $7,500 a year, with a $1,100 catch-up for those 50 and older. A 401(k)’s far higher ceiling is one real, practical reason many people use both account types together rather than choosing just one.

The Roth Income Limit That Doesn’t Apply to a Workplace Plan

This is a genuinely easy-to-miss distinction. A Roth IRA has an income phase-out: for 2026, eligibility to contribute directly phases out between $153,000 and $168,000 for single filers, and between $242,000 and $252,000 for married couples filing jointly, above those thresholds, direct Roth IRA contributions aren’t allowed at all. A Roth 401(k) offered through an employer, by contrast, carries no such income limit, meaning a higher earner who’s phased out of a Roth IRA can often still make Roth contributions inside a workplace 401(k) plan if their employer offers that option.

What This Means for Deciding Between Them

The practical takeaway isn’t “pick one,” it’s understanding that the two accounts solve different problems: a 401(k)’s higher contribution ceiling (and any employer match, which is essentially free money not available through an IRA) makes it the natural first stop for larger annual contributions, while an IRA’s broader investment choices (a 401(k) is limited to whatever a specific employer’s plan offers) make it worth using too, if income allows. Whether the traditional or Roth version of either makes more sense for a specific household’s real tax situation is exactly the kind of question worth a real conversation with a tax professional, not a generic online rule.

Sources: All 2026 contribution limits and Roth IRA income phase-out ranges sourced directly from Internal Revenue Service, “401(k) limit increases to $24,500 for 2026, IRA limit increases to $7,500.” The traditional-vs-Roth tax-timing distinction sourced from Internal Revenue Service, “Roth comparison chart.” Verified 2026-08-10.