An induction motor running at 1440 rpm on a 50 Hz supply has a slip speed of 60 rpm, as its synchronous speed is 1500 rpm but its actual rotor speed is 1440 rpm. The percentage slip is calculated to be 4%, found by taking the slip speed as a percentage of the synchronous speed. The slip reduces from 100% at standstill during starting towards 0% if the rotor could reach synchronous speed.