You're still underestimating the hours that are not billable. That plumber drives 15 minutes each way for a two hour job. That's a 20% loss of time. Plus it's not billable when the plumber has to go pick up materials from a hardware store. Nor is it billable when they deal with the overhead of running a business, maintaining accounts, dealing with bills, providing quotes, etc. Plus benefits are coming out of that $130. A self employed plumber working 40 billable hours/week is likely working more like 60 hours/week.