34 Pa. Code § 127.210 – Interest on untimely payments.

(a) If an insurer fails to pay the entire bill within 30 days of receipt of the required bills and medical reports, interest shall accrue on the due and unpaid balance at 10% per annum under section 406.1(a) of the act (77 P. S. § 717.1).
(b) If an insurer fails to pay any portion of a bill, interest shall accrue at 10% per annum on the unpaid balance.
(c) Interest shall accrue on unpaid medical bills even if an insurer initially denies liability for the bills if liability is later admitted or determined.
(d) Interest shall accrue on unpaid medical bills even if an insurer has filed a request for UR under Subchapter C (relating to medical treatment review) if a later determination is made that the insurer was liable for paying the bills.