It simply has to do with the number of lost/new employees in a year. So if you have 100 employees on your payroll and 100 quit over the course of a year, then you have 100% turnover. If 50, then 50/100 total employees = 50% turnover. It will be lower if less people left. Here’s the link where I learned this: https://www.aihr.com/blog/how-to-calculate-employee-turnover-rate/#:~:text=How to calculate annual turnover,%3D 0.05%2C or 5%25.