Originally Posted by HighFlight

Yes, a Roth 401K has higher limits, but I believe they are offset by the traditional 401K, are they not? So if one puts $15K into the 401K, then they could only put $3K (+ $6K if they are older) into the Roth 401K. Is this correct? Ish. Technically all of it is 401k, so you have an $18k contribution limit for both parts. As you say, if you contribute 15k to a traditional you could only contribute 3K to the Roth. But you COULD contribute 18k to the Roth and ignore the traditional entirely. Traditional and Roth IRA's work the same, 5,500 combined contribution limit between the two. The only caveat on the Roth 401k is the match remains traditional. That's required by the tax code and annoying but no net impact to you vs the traditional 401k

I like that the Roth 401K is post-tax, especially if one is younger. But it’s not as flexible as either a Roth IRA or a 401K, from my understanding. The Roth 401K must remain as it is, and cannot be converted down the road I think. A Roth 401k can be rolled over to a Roth IRA when you leave the company. The match would have to be rolled over to a Traditional IRA since it is tax deferred.

The main point is... contribute as much as you can afford, and start doing it last year! Absolutely!