24 Pa. Stat. § 584.3
Every person engaging in any business in any school district of the first class shall pay an annual tax at the rate of one (1) mill on each dollar of the annual receipts thereof, and beginning with the tax year 1968, and annually thereafter, shall pay an annual tax at the rate of two (2) mills on each dollar of the annual receipts thereof: Provided, however, That the amount payable shall not exceed two (2) per centum of his net income.
Where a receipt in its entirety cannot be subjected to the tax imposed by this act by reason of the provisions of the Constitution of the United States, or any other provision of law, the collector shall establish rules and regulations and methods of allocation and evaluation so that only that part of such receipt which is properly attributable and allocable to the doing of business in the school district levying the tax shall be taxed hereunder. The collector may make such allocation with due regard to the nature of the business concerned on the basis of mileage, division of the receipt according to the number of jurisdictions in which it may be taxed, the ratio of the value of the property or assets of the taxpayer owned and situated in the school district levying the tax to the total property or assets of the taxpayer wherever owned and situated, and any other method or methods of allocation other than the foregoing, calculated to effect a fair and proper allocation. Every person who ceases to carry on a business during any tax year shall be permitted to apportion his tax for such tax year on the basis of the number of months during which he did business.
24 P.S. § 584.3