1Part. 401k employee after-tax contribution source and timing

[spiritrider]

Accepting that a one-participant 401k is standard 401k, with a very short list of one-offs. I have a few questions with regards to employee after-tax contributions. Specifically, the contribution deadlines and source of the contributions. Let me start with the things I think I know and ask questions of the things I am not sure about.

Self-employed individuals can make their employee elective and employer contributions from personal funds on or before their tax filing deadline including extensions.

• Is there any reason that is not also true for employee after-tax contributions?

S-Corp 2% employer elective contributions are deducted from compensation not already received with a pay date on or before 12/31. The contribution must be deposited as soon as it can reasonably be segregated from the S-Corp's assets. The S-Corp has until its tax filing deadline including extensions to make its employer contributions.

Any ERISA 401k plan I am aware of that allows employee after-tax contributions, requires them be contributed from after-tax W-2 wages. However, I seem to remember conversations over the years, that nothing precludes direct employee after-tax contributions from personal funds provided that in the unlikely event the plan document and administrator procedures allow it.

1. Is the deadline for S-Corp 2% employee after-tax contributions 12/31 or the S-Corp's tax filing deadline including extensions?
2. Must the contributions be made from the S-Corp shareholder-employee's after-tax W-2 wages or can the contributions be made from personal funds?

[PensionPro]

prior discussion here.  contributing by personal check seems to be fine but no authority mentioned for an extension of time.