S.C. Code Ann. § 41-31-370: Interest on unpaid contributions.

(A) Contributions unpaid on the date on which they are due and payable, as prescribed by the department, shall bear interest at the rate of one percent for each month or fraction for which they remain unpaid but contributions as have accrued prior to the establishment of an employer's liability shall bear interest at the rate of one-half of one percent a month or fraction of a month, to the date on which liability is established, unless it is found by the department that the delay in the establishment of liability resulted from wilful negligence of the employer, and shall bear interest at the rate of one percent a month or fraction for which they remain unpaid thereafter.

(B) If any employer's amount of contributions which are due and payable, as prescribed by the department, are unpaid ten days following the date on which an assessment or debit memorandum was issued, a penalty of ten percent of the amount of contributions due and payable, not to exceed one thousand dollars, must be paid in addition to any other interest or penalty which may be applicable.

(C) The department may, for good cause, extend the time for the filing of reports and the payment of contributions. Any person to whom the extension is granted shall pay in addition to the contribution due, interest at the rate of one percent per month or fraction of a month from the due date of the contribution to the date of payment.