Hi Colette,
You can find the interest frequency under the following SPRO config. for FIAR
IMG-->Financial Accounting (New)-->Accounts receivable and Accounts payable---> Business Transactions--->Interest Calculation--->Interest Calculation Global Settings---->Prepare Account balance Interest Calculation.
Select the Interest Calculation Indicator and click on display.
In here you will be to set the Interest frequency (in months) for the Account.
Hope it helps
Thanks,
AB