How do you calculate profit on a repair job?

Take what you charged the customer and subtract three things, not two: the parts cost, the technician time (hours on the bench multiplied by what that hour costs you), and a share of your monthly overhead. Most shops stop after parts and labour, which is why a job that looks 40% profitable is often closer to 15%. Overhead — rent, electricity, software, admin salaries, insurance — is real money that has to come out of jobs, so divide your monthly overhead by the number of jobs you complete in a month and charge that to every ticket.