For delinquent payments to a Plan trust, we only look to actual earnings if the delinquent payments constitute an operational failure as well as a prohibited transaction. Delinquent payments do not always constitute both. For example, if a plan is an individually designed plan that we prepare, the delinquent payments will not constitute an operational failure as we do not include the DOL timing requirements in our documents (i.e., it would not in operation violate a term of the plan). Also, many prototype plan basic plan documents do not include the DOL timing requirements so there would be no operational failure in those.
If, however, there is an operational failure because there is a violation of the plan's terms, we advise providing participants with lost earnings in the amount of the greater of (i) the actual lost earnings computed as @Peter Gulia is suggesting and (ii) the lost earnings as computed on the DOL online calculator. The greater of amount is used to ensure that the correction meets both EPCRS and VFCP. However, this is extremely burdensome because when doing this the calculations have to be done on a per participant basis (while some affected participants may have had investment gains during the correction period others may have had losses so using lost earnings based on the DOL calculator for those with losses ensures that they receive some payment for the employer's use of the funds). Where the actual earnings are used for a participant's lost earnings, the VFCP submission would include a statement that the third-party recordkeeper has calculated actual lost earnings based on the participant's actual investments under the Plan from the loss date to the recovery date (or full payment date, if later, for earnings on earnings). This type of statement has never been rejected by the EBSA in a VFCP submission we have made involving corrections where there were both operational failures and prohibited transactions (this is not saying the EBSA wouldn't reject this type of statement on the next such filing we might submit).
Note though that if the delinquent payments only constitute a prohibited transaction and not an operational failure, the VFCP guidance does not provide for the use of the participant's actual investment earnings as a methodology for calculating lost earnings (actual earnings would be required if restored profits is required but that would be based on the amount the employer earned by using those funds in a specific investment, etc.). The VFCP guidance requires lost earnings to be based on the Code's underpayment rates.
A colleague noted to me that I put the link for the 2006 notice when I should have linked the 2025 notice. Sorry for that but note the substance is the same. Different subsection though §5(b)(6) instead of (5). See Federal Register :: Voluntary Fiduciary Correction Program
As alluded to above, what one agent will agree to may not be the same as what another agent will require.... depends on if they spilled their coffee going into work that morning or some other arbitrary happenstance....