If I contribute the max to a Roth 401k, is that taking $17.5k of my income in a year, taxing it, and then putting it in the Roth 401k? Or, do I get to contribute $20.5k 'pre-tax', pay the tax, and then end up with a max of $17.5k in the Roth 401k assuming I'm 15% tax bracket.
Does that question make sense? If it's the second way, you get to essentially squeeze more money into a Roth 401k than in a normal 401k.