72 Pa. Stat. § 3327
In order to receive the benefits of this act, any corporation may estimate the amount of the tax, or any portion thereof, which it deems it will become liable to pay under the provision of any revenue act referred to in section two of this act, on reports referred to in section three of this act, file such estimate with the Department of Revenue, and concurrently therewith pay into the State Treasury through the Department of Revenue on or before December fifteenth, one thousand nine hundred thirty-five, the amount of tax or any portion 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 tax and the proper report to be thereafter filed, in favor of the corporation paying the same, to the amount paid on account. In the adjustment and settlement of the tax accounts of the corporation on future reports filed, proper credits shall be allowed on each tax on which an advance payment has so been 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 on the books of the department. At the time a 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. § 3327