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.
Worked example: the same $10,000, three different retirement tax rates
Say you are in the 22% tax bracket and set aside $10,000 of pre-tax pay. In a traditional 401(k) the full $10,000 goes in. In a Roth 401(k) you pay the 22% tax first, so only $7,800 goes in. Assume both grow at 7% a year for 25 years, which multiplies the balance by about 5.43.
| Tax rate in retirement | Traditional (after tax) | Roth (tax-free) | Winner |
|---|---|---|---|
| 12% | $47,761 | $42,334 | Traditional |
| 22% | $42,334 | $42,334 | Tie |
| 32% | $36,906 | $42,334 | Roth |
The traditional balance grows to $54,274 before tax, and the Roth balance grows to $42,334 with no tax due. When your tax rate in retirement matches your rate today, the two come out identical. That is why the whole decision comes down to which rate you expect to be higher.
How to pick between them
- Early in your career or in a low bracket: a Roth usually makes sense, since you are likely to pay more tax later.
- At your peak earnings: the traditional deduction is worth the most when your bracket is highest.
- Not sure: split contributions between the two, if your plan offers both.
- Need cash flow now: traditional contributions lower your take-home pay by less than the same Roth amount does.
Limits, employer match and withdrawals
- The annual contribution limit applies to your Roth and traditional contributions combined, so you cannot contribute the maximum to each. The IRS adjusts the limit most years.
- Employer matching contributions have generally been made pre-tax, even when your own money goes into the Roth side. Some plans now let you take the match as Roth, so check with yours.
- Roth withdrawals are tax-free once you are 59½ and the account has been open for five years. Withdrawals from a traditional balance are taxed as ordinary income.
- Starting in 2024, Roth 401(k) balances no longer have required minimum distributions during your lifetime. Traditional balances still do.
Not sure how much you will have by retirement? Use the Retirement / 401(k) / Savings Goal Calculator to project your balance either way.