The date to remove excess deferrals is April 15, of the year following the contribution. The Apr 15 date is not the due date of the tax return, the tax law specifically says "April 15" but can even be before depending on the terms of the 401(k) plan. The IRS's delay of the filing date to May 17 did not change the tax law.
See internal Revenue Code 26 CFR § 1.402(g)-1(e)(2)(i)
(2) Correction of excess deferrals after the taxable year. A plan may provide that if any amount is an excess deferral under paragraph (a) of this section:
(i) Not later than the first April 15 (or such earlier date specified in the plan) following the close of the individual's taxable year,
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
