401k vs Roth 401k Comparison Calculator

How the 401k vs Roth 401k Calculator Works

This calculator projects the after-tax retirement value of both the traditional (pre-tax) 401k and the Roth (after-tax) 401k using the same annual contribution amount and expected market return. The key difference is when you pay taxes: traditional 401k contributions are made before tax, reducing your taxable income today, but withdrawals in retirement are fully taxed as ordinary income. Roth 401k contributions are made with after-tax dollars, so qualified withdrawals in retirement are completely tax-free.

The calculator applies the standard future value of an annuity formula — C × ((1 + r)^n − 1) / r — where C is the annual contribution, r is the annual return rate, and n is the number of years. For the traditional 401k, tax is applied at your estimated retirement tax rate on withdrawal. For the Roth 401k, the effective contribution is reduced by your current tax rate (since you pay tax first), but the final balance is entirely tax-free. The winner is determined by comparing the after-tax dollar amounts side by side. Last updated: March 2026 using 2025 IRS contribution limits.

When Traditional 401k Beats Roth 401k

The traditional 401k wins when your current marginal tax rate is higher than your expected retirement tax rate. If you are in the 32% bracket now but expect to be in the 22% bracket in retirement, deferring taxes makes financial sense — you pay less tax on the same dollars. This is common for peak-earning professionals in their 40s and 50s who expect significant income reduction in retirement. High earners in states with steep income taxes often benefit from traditional contributions if they plan to retire in a lower-tax state.

Traditional 401k also has an immediate cash flow advantage: your out-of-pocket cost is lower each year because you contribute pre-tax dollars. Investing the tax savings separately can amplify the long-term advantage. Additionally, if you expect lower Social Security income or will rely primarily on 401k withdrawals, your effective retirement tax rate is often lower than your working tax rate due to standard deductions and lower total income.

When Roth 401k Wins Over Traditional 401k

The Roth 401k wins when your current marginal tax rate is lower than your expected retirement tax rate. Young professionals early in their career — often in the 10% or 12% bracket — benefit most from locking in today's low tax rate. Future tax rates are uncertain; many financial planners recommend at least some Roth savings as a hedge against potential rate increases. The Tax Cuts and Jobs Act rates expire after 2025, and future legislation could raise rates significantly.

Roth 401k also has unique advantages: qualified withdrawals do not count as taxable income, which can reduce Medicare premium surcharges (IRMAA), preserve Social Security benefit taxation thresholds, and enable more flexible withdrawal strategies in retirement. Unlike the Roth IRA, the Roth 401k has no income limit — high earners who are ineligible for a Roth IRA can still contribute to a Roth 401k. This makes it especially valuable for those earning above the Roth IRA phase-out range ($150,000 single / $236,000 married in 2025).

Contribution Limits and Key Rules for 2025

For 2025, the IRS sets the 401k contribution limit at $23,000 for employees under age 50. If you are age 50 or older, the catch-up contribution limit is an additional $7,500, bringing the total to $30,500. This combined limit applies across both traditional and Roth 401k contributions — you cannot contribute $23,000 to each; it is $23,000 total split however you choose.

Important rules to know: employer matching contributions are always deposited as pre-tax traditional 401k contributions, even if you choose Roth 401k for your personal contributions — you effectively get tax diversification automatically. Required Minimum Distributions (RMDs) apply to Roth 401k accounts at age 73 (unlike Roth IRA which has no RMDs) unless rolled over to a Roth IRA. Most financial advisors recommend a tax diversification strategy: splitting contributions between traditional and Roth so you have flexibility to draw from whichever account is more advantageous year by year in retirement.