I am a "freelancer". I have discovered that billing by the hour is the worst idea. It creates the inherent conflict. Clients start resenting how much time it took you, etc. Instead always bill per job, unless impossible to estimate. Determine value acceptable to you and the client. Agree on lump sum and let chip fall where they may. Sometimes client wins, sometimes you win, in the end it all events out. More importantly you build a base for the next job where everyone agrees to acceptable fixed fee parameters and you can correct the fee estimate. Hourly billing is really wrong in my opinion.