How to know whether a project was truly profitable

Start with revenue, deduct external costs, travel, materials and suppliers, then compare the result with the real hours of everyone involved.

Divide the net income attributable to the project by the time actually invested. It does not replace your rate, but it shows which projects are consuming more effort than planned.

One project can be an exception. Repeated deviations often reveal an issue with scope, revisions, approval or estimation worth fixing.