Is there any reason that, as long as the plan document does not contain language preventing it, a 401(k) plan participant could not defer any $ amount up to the 402(g) limit from a single paycheck (presuming the paycheck is large enough)? So it would be theoretically possible for a 401(k) plan to allow a participant to defer $10,500 - or whatever the 402(g) limit is for the year - out of the participant's first paycheck for the year?

If participant then quits after this large deferral you could have a 415 problem and it may play havoc with your ADP test if employee is an HCE.

Otherwise it would seem to be o.k. Haven't looked to see whether this is a 401(a)(4) benefit right and feature so that you would have to be clear that everyone (or at least the required number of NHCE's) could do it.

I had a client once that paid large annual bonuses early in the year. Participant received a $1million bonus off a non-system check. Payroll records indicated that the participant had elected to defer at a 10% rate, so they withheld and contributed $100,000 to the plan. We fixed that awfully quickly.

General answer is that the entire 402(g) limit could be contributed with first payroll, unless there is a plan provision to the contrary (e.g. max percent of pay that can be contributed per pay period).