72 Pa. Stat. § 3333
In order to receive the benefits of this act, any corporation may make any estimate of the amount of the tax, or any part thereof, which it deems it will become liable to pay under the provisions of any revenue act referred to in this act, file such estimate with the Department of Revenue, and pay into the State Treasury through the Department of Revenue on or before December fifteenth, one thousand nine hundred and thirty-five, the amount of tax, or any part thereof, to which it agrees it will become liable. Such estimates shall be made on forms prepared and furnished by the Department of Revenue. Upon the receipt of any such advance payment of tax, the Department of Revenue shall establish a credit on its books, with respect to the proper report to be thereafter filed, in favor of the corporation paying the same, to the amount of tax paid on account, and, in the settlement of the tax accounts of the corporation on future reports filed, proper credits shall be allowed on each settlement on which an advance payment has been so made. The department shall issue its receipt, evidencing payment on account of taxes under the provisions of this act, which shall show the amount of tax paid in advance and the total credit established. At the time the corporation finally pays any balance due on any taxes on which an advance payment was made, the discount for the advance payment shall be allowed by the Department of Revenue and be deducted from the balance due by the corporation.
72 P.S. § 3333