401(k) vs Roth IRA: Which Should You Use?

Written by Jim Norris · NorrisAI AlphaLens · Updated August 2026

Quick answer: A 401(k) is an employer-sponsored retirement plan where contributions reduce your taxable income today — you pay taxes when you withdraw in retirement. A Roth IRA is an individual account funded with after-tax money — you pay taxes now, but withdrawals in retirement are completely tax-free. Most people benefit from using both. The sequence that maximizes results for most investors: 401(k) up to the employer match → Roth IRA to the annual limit → back to 401(k) for additional contributions.

Key differences at a glance

When the 401(k) wins

You expect to be in a lower tax bracket in retirement. The 401(k)'s pre-tax benefit is most valuable when your current tax rate is higher than your future rate. If you're in a high income year now and expect lower income in retirement, the traditional 401(k) saves you more in taxes overall.

Your employer offers a match. The match makes the 401(k) unbeatable up to the match threshold — it's an instant return no other account can deliver.

You want to reduce your taxable income now. 401(k) contributions lower your adjusted gross income, which can affect eligibility for other tax benefits.

When the Roth IRA wins

You expect to be in a higher tax bracket in retirement. Paying taxes now at a lower rate and getting tax-free growth later is the Roth's core advantage. Young investors early in their careers — typically at lower income levels — often benefit most from locking in low tax rates now.

You want tax diversification. Having both pre-tax (401k) and after-tax (Roth) accounts gives you flexibility in retirement to manage your taxable income strategically.

You want flexibility. Roth IRA contributions (not earnings) can be withdrawn at any time without penalty — useful if you might need access before retirement.

You want to leave money to heirs. Roth IRAs have no required minimum distributions and pass tax-free to beneficiaries.

The income limit for Roth IRA

In 2026, Roth IRA contributions phase out for single filers above roughly $150,000 and for married filers above roughly $236,000 in modified adjusted gross income. Above these limits, a "backdoor Roth IRA" conversion strategy may be available — consult a tax professional.

The optimal sequence for most investors

1. Contribute to 401(k) up to the full employer match. Free money first, always.
2. Max out your Roth IRA ($7,000 in 2026 if eligible). Tax-free growth is extremely valuable over decades.
3. Return to 401(k) and contribute up to the annual limit if you have more to invest.
4. Taxable brokerage account for additional investing beyond retirement account limits.

Professor Jeremy Siegel of the Wharton School emphasizes that tax-advantaged accounts are one of the most powerful tools available to individual investors — the compounding effect of tax-free or tax-deferred growth over decades is enormous. Maxing these accounts before investing in taxable accounts is almost always the right priority. — Stocks for the Long Run, McGraw-Hill

Professor Burton Malkiel of Princeton University advocates for tax diversification — holding both traditional and Roth accounts — so that in retirement you have flexibility to draw from whichever source minimizes your tax bill in any given year. That optionality has real value that's hard to model precisely in advance. — A Random Walk Down Wall Street, W.W. Norton

Where to go deeper

For a detailed walkthrough of each research framework, see the complete guide to all 15 AlphaLens frameworks.

For definitions of investing terms, see the AlphaLens investing glossary.