15 Pa.C.S. § 5588

If a bond or other obligation for the payment of money is acquired as an investment for any common trust fund at a cost in excess of the par or maturity value thereof, the nonprofit corporation may, during but not beyond the period that the obligation is held as an investment in the fund, amortize the excess cost out of the income on the obligation, by deducting from each payment of income and adding to principal an amount equal to the sum obtained by dividing the excess cost by the number of periodic payments of income to accrue on the obligation from the date of the acquisition until its maturity date.