We've added a Prepayment Rate field to the Product Prepayment Options in the Administration Section. In addition, a Prepayment Rate can be set for the "None" Prepayment Option:
A Prepayment Rate indicates the rate, expressed as a percentage, of the balance that is anticipated to be paid off on top of the normal amortization. For example, a 4.0% Prepayment Rate would indicate that on average, an extra 4% of the balance of the year will be prepaid. The Prepayment Rate is not visible in the Opportunity Screen, and is not presented in the Advanced Analytics Amortization table. These fields will not be visibly changed; however, selecting a prepayment option with a prepayment rate attached to an opportunity will affect the opportunity's ROE.