72 Pa. Stat. § 806
All taxes due the Commonwealth shall bear simple interest from the date they become due and payable until paid. The interest rate per annum during each calendar year shall be the interest rate established by the Secretary of the Treasury of the United States under the provisions of the Internal Revenue Code of 1954, effective January 1 of such calendar year without regard to any change or changes in said Federal interest rate during such calendar year. No penalties shall bear any interest whatsoever. The payment of interest, as aforesaid, shall not relieve any person from any of the penalties, commissions or additional tax prescribed by law for neglect or refusal to furnish timely returns or reports to the Department of Revenue, or to pay any claim due to the Commonwealth from such person. The Secretary of Revenue shall publish the rate of interest for each calendar year in the Pennsylvania Bulletin. In the case of any tentative tax, estimated tax or installment payment, interest shall run on any unpaid amount from the last day the payment is due to the date paid. In the case of tax which is resettled as a result of a final change or correction of taxable income by the Commissioner of Internal Revenue or any other agency or court of the United States, interest shall be computed on any additional tax due from thirty (30) days after the corporation receives notice of such final change or correction until paid.
Whenever the tax liability of a person is so affected by any payment or credit, settlement or resettlement, assessment or reassessment or determination or redetermination as to change the interest liability of such person, such interest liability shall be recomputed and adjusted by the Department of Revenue and approved by the Department of the Auditor General in cases in which said latter department is required to approve settlements and resettlements, so as to correspond to the tax liability as changed, without the necessity for the filing of any petition or request by such person or by said departments.
72 P.S. § 806