What this calculator does
Many 401(k) plans let you choose traditional (pre-tax) contributions, Roth (after-tax) contributions, or both. Enter your pay, how much you put in, your age and your expected tax rate in retirement, and the calculator shows which choice leaves you more after taxes, when both cost your paycheck the same today.
How it is worked out
A traditional contribution lowers this year's federal income tax. The calculator works out that saving with the 2026 brackets and standard deduction. A Roth contribution of the same cost to your paycheck is the traditional amount minus that saving. Both grow at the same return. At retirement, the traditional balance is reduced by your retirement tax rate; qualified Roth withdrawals are tax-free.
Example: a single person earning $75,000 puts 10%, or $7,500, into a traditional 401(k), which saves $1,650 of 2026 federal tax (22%). The same paycheck cost buys $5,850 of Roth contributions. After 30 years at 6%, the traditional account holds about $628,500, or about $553,100 after a 12% retirement tax rate; the Roth holds about $490,200, tax-free. Here the traditional wins because 12% is lower than the 22% saved today. With a retirement rate above 22%, the Roth would win.
2026 limits and rules
- Your own contributions, traditional and Roth together, are limited to $24,500 in 2026, plus $8,000 from age 50 or $11,250 at ages 60 to 63 (IRS).
- Unlike a Roth IRA, a Roth 401(k) has no income limit.
- From 2026, people whose 2025 Social Security wages from the employer were over $150,000 must make catch-up contributions as Roth.
- Employer matching contributions are usually pre-tax and taxed when you take them out, whichever you choose.
Frequently asked questions
Is a Roth or traditional 401(k) better?
At the same cost to your paycheck, a Roth is better if your tax rate in retirement will be higher than the rate you save now, and a traditional is better if it will be lower. If you are not sure, splitting between both spreads the risk.
Can I contribute to both a Roth and a traditional 401(k)?
Yes, if your plan offers both, but the $24,500 limit for 2026 (plus any catch-up) covers both together.
Is there an income limit for a Roth 401(k)?
No. Income limits apply to Roth IRAs, not to Roth contributions in a 401(k).
When are Roth 401(k) withdrawals tax-free?
When they are qualified: generally after age 59½ and at least five years after your first Roth contribution to the plan.
Is my information saved?
No. The numbers stay on this page.