@dmertz wrote:
Opus 17 is correct. The excess Roth 401(k) contribution and attributable earnings will be taxable upon eventual distribution, with the first amounts out being the excess and its attributable earnings.
See Designated Roth Contributions as Excess Deferrals in T.D. 9324 2007-22 I.R.B 1302:
https://www.irs.gov/irb/2007-22_IRB#TD-9324
The fact that it is first-out rather than pro-rata makes it easier to keep track of and to handle when you retire.
Thanks.
