Roth 401(k) vs. Traditional 401(k): What's the Real Difference?
The core tax difference between a Roth 401(k) and a traditional 401(k), how it affects your paycheck and retirement withdrawals, and how to think about which to choose.
Roth and traditional 401(k) accounts hold the same investments and follow the same contribution limits — the entire difference comes down to when you pay income tax on the money.
| Traditional 401(k) | Roth 401(k) | |
|---|---|---|
| Contributions | Pre-tax — reduces taxable income now | After-tax — no upfront tax break |
| Growth | Tax-deferred | Tax-free |
| Withdrawals in retirement | Taxed as ordinary income | Tax-free (if qualified) |
| Best fit when | You expect a lower tax rate in retirement than now | You expect a similar or higher tax rate in retirement than now |
Why the comparison isn't about which account "grows more"
Given identical contribution amounts and returns, a Roth and traditional 401(k) grow to the same pre-tax figure — the difference only shows up at withdrawal, when traditional balances are taxed and Roth balances generally aren't. That means the real decision hinges on comparing your current tax rate against your expected tax rate in retirement, not on projected growth.
A common middle-ground approach
Many savers split contributions between both account types (where their plan allows it) to hedge against uncertainty about future tax rates and tax law changes, rather than betting entirely on one prediction.
Either way, the growth math is identical — project your contributions, employer match (which is generally pre-tax regardless of your own account type), and expected return with the Retirement / 401(k) / Savings Goal Calculator to see your projected balance either way.