The goal of this article is to provide guidance on teacher attrition rates that can inform power analyses. The subjects were a nationally representative sample of teachers responding to the National Center for Education Statistics Schools and Staffing Survey and Teacher Follow-Up Survey (2011-2013). The findings indicate that at the national average of percent free and reduced-price lunch (FRL), approximately one in six teachers move schools or leave the profession between adjacent academic years. The odds of this type of attrition happening increase by approximately 0.8% for each 1% FRL difference (increase) of a planned study context from the national average.