Employee turnover rate is pretty simple to calculate: take the number of employees who left during a specific period, divide it by the average number of employees in that same period, and multiply by 100. For example, if 10 people left over a year and your average staff count was 100, your turnover rate is 10%. I usually calculate the average by adding the starting and ending headcounts and dividing by 2. It keeps things quick and fairly accurate.