How the employer match complicates this
Unlike IRAs, the 401(k) has an employer match. Historically, the match went to the Traditional side regardless of whether you chose Traditional or Roth 401(k). SECURE 2.0 (signed December 2022) lets plans direct the match to Roth, but it makes the match immediately taxable to you as ordinary income. Most plans still default the match to Traditional.
This matters for the comparison: a Roth 401(k) is really "Roth employee money + Traditional employer money" for most plans. The calculator above assumes the match goes Traditional either way, so the Roth 401(k) path shows Roth growth on your contributions plus tax-deferred growth on the match — a common real-world scenario.
Worked example: $23,500 contribution, $6,000 match, 25 years
At 24% now and 22% in retirement, 7% return: Traditional 401(k) grows to $1,870,000 combined balance, worth $1,458,600 after 22% retirement tax. Roth 401(k) grows to the same $1,870,000, but only the $1,484,000 Roth portion is tax-free; the $386,000 match piece is taxed at 22% = $301,100 after tax. Total Roth path: $1,785,100 after tax — a $326,500 advantage over Traditional.
The Traditional gave you $5,640/year in tax savings ($141,000 over 25 years). If you reinvested that at 7% with 15% tax drag, it would grow to roughly $280,000 — close to but not fully closing the Roth gap.
Key caveat: this assumes the 22% bracket in retirement. If you are certain you will drop to the 12% bracket in retirement, Traditional wins by roughly $150,000. The Roth advantage is largely about bracket protection, not certainty.
The contribution limit trick
A Traditional 401(k) saves the same dollar amount as a Roth 401(k) — but the Traditional lets the same dollar amount hit your paycheck less painfully because of the deduction. In other words, if you can afford to contribute $23,500 to a Traditional, you can only afford roughly $17,860 to a Roth (both reducing take-home by the same amount after tax).
If you are at the contribution limit and can pay the extra tax out of pocket, the Roth is a stealth higher contribution — you are effectively saving more in tax-advantaged space. This is the strongest argument for Roth for high earners who can afford it: you get more tax-advantaged real dollars inside the account.
Our default recommendation
For a 35-year-old in the 24% bracket expecting 22%–28% in retirement: Roth 401(k) if you can afford the tax hit out of pocket. Otherwise, Traditional 401(k) and redirect the tax savings into an IRA or taxable account. The worst outcome is Traditional 401(k) with the tax savings spent — you lose the tax-arbitrage benefit.
For a 50-year-old in the 32% bracket planning to retire at 60: Traditional 401(k), because you have a ~10-year window to convert to Roth at lower brackets between retirement and age 73 RMDs. Park the pre-tax money, then convert strategically.
For anyone in the 12%–22% bracket with a long runway: Roth 401(k). The bracket insurance is worth the forgone deduction.