From the folks at Vanguard:
“When it first became available to defined contribution plans in 2005, the Roth 401(k) was seen by many retirement experts as a vehicle that would mostly benefit highly compensated workers. While there are many reasons why the Roth 401(k) may be an attractive option for higher-income employees, what has surprised many about this innovative plan feature are the benefits it offers participants across the income spectrum, making it advantageous for a wide range of employees and plans.
“In contrast to traditional 401(k) plans in which participants make contributions on a pre-tax basis and don’t pay taxes until they make withdrawals in retirement, the Roth 401(k) allows participants to pay taxes on their retirement savings contributions up front and avoid future taxes on their plan savings in retirement. All withdrawals of Roth savings are free from federal income tax in retirement as long as the participant is at least 59½ years old and their account has been open for at least five years. Participants in plans that offer the Roth feature can choose to make their contributions on a pre-tax basis, a Roth basis, or some combination of the two.”
Click here to read the full article, including a chart comparing pre-tax 401(k) contributions with Roth 401(k) contributions.