Employee Roth elections not withheld correctly for 2024

An audited plan just told me today that there are 13 employees that did not have the correct amount of Roth withheld based on their elections.  The amount withheld was based on the after-tax net pay, not gross pay. 

From what I'm reading since it is just past 9-15 the missed Roth needs to be contributed AND QNEC equal to 50% of the missed Roth plus earnings.

Any ideas as to best way to credit lost earnings - so it is probably 26 pays, 13 employees.  SO I will find a way to estimate plan earnings - perhaps look at the entire plan earnings for the year reduce 50% since missed evenly through the year.

Thank you for any assitance.

Tom

I've misread that rule the same way you did, LOL.  9.5 months after the end of the year is October 15th. I've definitely fallen into the trap of "oh half way through the 9th month is 9.5 months."  9.5 months is ALL of September and half of Octboer.

I assume you are talking about the deadline for missed deferrals on a plan with auto enrollment, correct?

As for lost earnings, I think the easiest and adequate approach is plan rate of return.  

I wonder if your client and a client of mine had the same payroll systm.  Literally the exact same thing happened to my client.  It was bazaar and I kept asking how could this be?? But it be.  It was a big correction for me, spanned a few years.  Real nightmare.  Had to recalculate the match too.