How much interest do I have to pay my renter on her escrow deposit when she leaves, I live in PA

You would have deposited her money into the local bank and paid her the interest that was paid from a normal savings account.

You did deposit it ?

You probably don't have to pay interest unless the lease or escrow agreement provides for interest.

But if you do owe interest, that's why many trust account agreements provide for deposit in a non-interest bearing account. It's a complicated calculation, and most lawyers don't have the intelligence or patience to do the math.

For every month (or other period for which you receive statements from the bank), multiply the interest received on the account in that month by a ratio (of the amount of the deposit to the total amount in the account). Cumulate the result for each month.

PA law requires that interest on the security deposit be paid to the tenant after 2 years. However the landlord is entitled to retain 1% of that interest for administrative expenses. However the law does not state the rate of interest to be paid.

To the OP: You can pay the tenant interest at whatever rate local banks are paying on interest-bearing savings accounts. You are entitled to retain 1% of that interest.

Here is the applicable law:

Section 250.511b. Interest on escrow funds held more than two years
(a) Except as otherwise provided in this section, all funds over one hundred dollars ($100) deposited with a lessor to secure the execution of a rental agreement on residential property in accordance with section 511.18 and pursuant to any lease newly executed or reexecuted after the effective date of this act shall be deposited in an escrow account of an institution regulated by the Federal Reserve Board, the Federal Home Loan Bank Board, Comptroller of the Currency, or the Pennsylvania Department of Banking. When any funds are deposited in any escrow account, interest-bearing or noninterest-bearing, the lessor shall thereupon notify in writing each of the tenants making any such deposit, giving the name and address of the banking institution in which such deposits are held, and the amount of such deposits.
(b) Whenever any money is required to be deposited in an interest-bearing escrow savings account, in accordance with section 511.1, then the lessor shall be entitled to receive as administrative expenses, a sum equivalent to one per cent per annum upon the security money so deposited, which shall be in lieu of all other administrative and custodial expenses. The balance of the interest paid shall be the money of the tenant making the deposit and will be paid to said tenant annually upon the anniversary date of the commencement of his lease.
(c) The provisions of this section shall apply only after the second anniversary of the deposit of escrow funds.