The basic difference between a traditional 401(k) and a Roth 401(k) account is the tax treatment. With a traditional 401(k) account, you make contributions with pre-tax dollars, so you get a tax break up front, helping to lower your current income tax bill. With a Roth 401(k), it's basically the opposite. You make your contributions with after-tax dollars, meaning there is no upfront tax deduction. However, Roth 401(k) withdrawals of both contributions and earnings are tax-free at age 59.5 if you have held the account for five years in a Roth 401(k) account.