29 CFR § 4007.7 - Late payment interest charges.
(a) If any premium payment due under this part is not paid by the due date prescribed for such payment by this part, an interest charge will accrue on the unpaid amount at the rate imposed under section 6601(a) of the Code for the period from the date payment is due to the date payment is made. Late payment interest charges are compounded daily.
(b) With respect to any PBGC bill for a premium underpayment and/or interest thereon, interest will accrue only until the date of the bill if the premium underpayment and interest billed are paid within 30 days after the date of the bill.
The following state regulations pages link to this page.