Roth 401(k) contributions have the same limits as regular 401(k) contributions.
The contribution limits for your Roth 401(k) are the same as the contribution limits for a traditional 401(k), which, in 2016, is $18,000, but these limits are adjusted upwards to account for inflation. If you’re over 50, you can add a catch-up contribution of $6,000 on top of the $18,000 for a total contribution of $24,000.
It is important to note that these figures represent the total contribution which can be made by an employee to either of these vehicles in a given year. A participant under 50 years old who made pretax 401(k) contributions of $12,000 would only be permitted to contribute $6,000 to a Roth 401(k) that year, for a total of $18,000 in possible contributions.
It’s good to know, also, that it is possible to contribute to both a 401(k) and IRA in the same year, but traditional IRA deductions and Roth IRA eligibility get phased out at certain income levels when an individual or the individual’s spouse has a qualified plan at work.