A Single Loss Expectancy (SLE) is the value in dollar ($) that is assigned to a single event. The SLE can be calculated by the following formula: SLE = Asset Value ($) X Exposure Factor (EF) The Exposure Factor (EF) represents the % of assets loss caused by a threat. The EF is required to calculate the Single Loss Expectancy (SLE). The Annualized Loss Expectancy (ALE) can be calculated by multiplying the Single Loss Expectancy (SLE) with the Annualized Rate of Occurrence (ARO). Annualized Loss Expectancy (ALE) = Single Loss Expectancy (SLE) X Annualized Rate of Occurrence (ARO) Annualized Rate of Occurrence (ARO) is a number that represents the estimated frequency in which a threat is expected to occur. It is calculated based upon the probability of the event occurring and the number of employees that could make that event occur.