Function/Procedure to calculate due date based on transaction date

Receivables calculates invoice due date based on the transaction date and payment terms on the invoice. Does anyone know what function/procedure within the standard Oracle package is used to calculate this due date. We want to leverage this function in one of our custom reports. We were thinking of passing a date and payment terms to this function and get the due date which would then be used for further calculations on the report. The transaction that we are trying to show on this report are not yet converted to invoices but are open sales orders which is why we