Traditional vs Roth — how to choose
Both grow tax-free. The difference is when you're taxed: a Traditional 401(k)/IRA gives you a deduction today and is taxed at withdrawal; a Roth uses after-tax money now and is never taxed again.
The one rule that decides it
From the same after-tax dollars, the Traditional account ends up worth the Roth amount times (1 − retirement tax rate) ÷ (1 − current tax rate):
- Traditional wins if your tax rate will be lower in retirement.
- Roth wins if your tax rate will be higher in retirement.
- Tie if they're equal.
Because the deduction is worth your marginal rate, your current income and state matter — this tool pulls the real 2026 federal + state marginal rates for both points in time.
Get the employer match first
Before the traditional-versus-Roth question matters at all, there is a step that beats both: if your employer matches contributions, contribute at least enough to capture the full match. A 50% match is an immediate 50% return on that money, which no tax-treatment argument comes close to. Employer matching contributions are generally made on a pre-tax basis and grow tax-deferred, so they are taxable on withdrawal even if your own contributions are Roth.
Why "I will be in a lower bracket in retirement" is often wrong
The traditional 401(k) wins when your rate in retirement is lower than your rate today, and most people assume theirs will be. Several things push the other way. Required minimum distributions force taxable withdrawals from tax-deferred accounts later in life whether you need the money or not. Social Security benefits can become partly taxable depending on your other income. A paid-off house and grown children mean fewer deductions than during your working years. And tax rates themselves are set by legislation that changes.
None of that makes the Roth automatically better. It means the comparison deserves an honest estimate of your retirement rate rather than an assumption, and that spreading money across both treatments has genuine value as a hedge against being wrong.
Tax diversification
Holding both traditional and Roth balances gives you something valuable in retirement: control over your taxable income each year. You can draw from the traditional account up to the top of a favourable bracket and take anything further from the Roth, which can keep you under thresholds that affect Medicare premiums and the taxation of Social Security. Someone with only tax-deferred savings has no such lever.
Other differences worth knowing
- Contribution limits are shared. The annual employee deferral limit applies across your traditional and Roth 401(k) contributions combined, not to each separately. Check the current year's limit with the IRS, since it is indexed.
- Roth 401(k) and Roth IRA are different accounts with different rules, including income limits that apply to the IRA but not to the 401(k). A high earner locked out of a Roth IRA can usually still make Roth 401(k) contributions.
- Early withdrawals are penalised in both, with limited exceptions. Neither is an emergency fund.
- The deduction is worth your marginal rate. A traditional contribution made in a low-income year is worth less than the same contribution in a high-income year, which is worth remembering early in a career.
Frequently asked questions
Which should I pick?
High earners now who expect lower retirement income often favor Traditional. Younger or lower-bracket savers, or those expecting high retirement income, often favor Roth — plus Roth gives tax-free, flexible withdrawals. The calculator shows the dollar difference for you.
Can I use both?
Yes — many people split contributions to hedge against future tax-rate uncertainty.