Did that job make money?
The version of this calculation most people do in their head leaves out payroll burden and overhead, which is why jobs that felt profitable were not. This one includes both.
Result
Run this on a job you thought went well and a job you know went badly. The gap between the two is usually a production rate in your catalog that is wrong, and it is wrong on every future quote until you change it.
Questions
Why allocate overhead to a single job?
Because overhead happens regardless, and a job that does not carry its share of it is being subsidised by the others. A job can be gross-profitable and still lose money.
Where do I get the actual hours?
From a clock attached to the job. Reconstructing them on Friday from memory is how jobs stay mysteriously unprofitable.
Or stop doing this in a calculator
Aerys prices the whole job from your own catalog and production rates, sends it with an accept link and an invoice already attached, and then tracks what the job actually cost against what you quoted.