71 Pa. C.S. § 5939
The interest reserve account shall be the ledger account to which shall be credited all income earned by the fund and to which shall be charged all administrative and investment expenses incurred by the fund. At the end of each year the required interest shall be transferred from the interest reserve account to the credit of each of the accounts of the fund in accordance with the provisions of this subchapter. In addition, at the end of each accounting period, the interest reserve account shall be credited or charged with all recognized changes in the market valuation of the investments of the fund. The administrative and investment expenses of the board relating to the administration of the system and investments of the fund shall be paid from the fund out of earnings. Any surplus or deficit in the interest reserve account at the end of each year shall be transferred to the state accumulation account.
71 Pa.C.S. § 5939