Experience modifier or experience modification is a term used in the American insurance business and more specifically in workers' compensation insurance. It is the adjustment of annual premium based on previous loss experience. Usually three years of loss experience are used to determine the experience modifier for a workers' compensation policy. The three years typically include not the immediate past year, but the three prior. For instance, if a policy expired on January 1, 2007, the data included on the Experience modification would comprise the period from January 1, 2003 to January 1, 2006.