Reviewed September 2026.
A traditional 401(k) deferral lowers taxable wages now; withdrawals are generally taxed as ordinary income later. A Roth 401(k) (designated Roth) uses after-tax deferrals; qualified withdrawals of contributions and earnings are generally tax-free. Qualified usually means the Roth account has met the five-taxable-year participation clock and the distribution is made after age 59½, death, or disability (confirm current IRS designated-Roth rules). Most employer matches still land in a pre-tax bucket even when you elect Roth deferrals. This guide is the workplace plan choice. IRA-only tax timing: Roth vs traditional IRA taxes. First-dollar map: Roth IRA vs 401(k) starter.
What actually differs on your paycheck
| Feature | Traditional 401(k) | Roth 401(k) |
|---|---|---|
| Paycheck today | Deferral reduces taxable wages | Deferral taken after tax; take-home falls more for the same % |
| Growth | Tax-deferred | Tax-free if qualified distribution rules met |
| Withdrawals in retirement | Ordinary income (pre-tax) | Tax-free if qualified |
| Employer match | Usually pre-tax (confirm SPD) | Usually still pre-tax |
| Lifetime RMDs (owner) | Required at the statutory age | No lifetime RMDs for the original owner under current IRS rules after SECURE 2.0 (confirm plan paperwork) |
Contribution dollar limits are shared across traditional and Roth deferrals inside the same plan. Catch-up rules for age 50+ sit on top of the employee deferral limit (Catch-up contributions).
Worked sketch: $10,000 deferral, 24% bracket
Jordan earns wages in the 24% federal bracket and can defer $10,000 this year.
| Election | Approx federal tax effect this year | Account type |
|---|---|---|
| Traditional $10,000 | Roughly $2,400 less federal tax this year (bracket × deferral; ignores FICA/state) | Pre-tax balance grows |
| Roth $10,000 | No federal deduction; Jordan pays tax on the wages used to fund it | Roth balance grows |
If Jordan expects a higher marginal rate in retirement (large pension, small deductions, high provisional income), Roth deferrals can buy tax-free withdrawals later. If Jordan expects a lower rate later, traditional often wins on current tax savings. Many people split (for example 50/50) when the future bracket is unclear.
Match still matters more than the Roth/traditional split when you are below the full match: Employer match on 401(k). Later conversions are a separate lever: Roth conversions basics.
Decision cues (not advice)
- Need lower taxable income this year (student loan IDR, Marketplace premiums, phaseouts)? Traditional may help.
- Early-career, lower bracket now, long horizon? Roth often looks attractive.
- Already maxing a Roth IRA and want more Roth space? Roth 401(k) adds room without IRA income caps.
- Want flexibility for future RMDs and tax brackets? Mixing buckets helps.
Filing context: Filing taxes for beginners.
Checklist
- Confirm the plan offers designated Roth, traditional, or both.
- Capture the full match before optimizing Roth vs traditional.
- Estimate this year’s marginal rate vs a plausible retirement rate.
- Decide a split percentage and revisit after raises or tax-law changes.
- Recheck beneficiaries and investment elections after you switch sources.
Educational only. Not tax or investment advice. Plan menus, match formulas, and RMD rules change; confirm with the plan administrator, IRS publications, and a qualified professional.