But you're also forgetting that this 3-5 hours has basically made you lose what could have been 4 hours at another client because they've taken up your time in your schedule. This is your per-job overheads.

Your utilisation is your client's problem, not yours. Don't let your rate be tied to your time, make it tied to your skills and your value to the business and force yourself to be worth that value.

Don't let yourself lose out in the name of "being competitive". Bill half the day if you have to leave early and consider it a half day off, but never bill hourly.

Source: just went from billing hourly to daily. I feel so much better now, especially when you realise people are willing to pay if you're worth it.

Last year I was on a no-questions, no deviating day-rate. The consultancy I was working through wanted hourly accounting, I told them no and charged my rate per day or part of a day I worked for them, and based my working practices around 7.5 hour days. I put in the odd extra hour or ten here and there because I liked them and enjoyed the project, and they never quibbled about me clocking off early when the project didn't require a full day's attention. Quid pro quo I guess.

For this current contract the agent demands an account of hours worked and pays extra hours at day-rate/7.5, up until some maximum at which time I get to charge double, but the time has to be authorised by the end-client.

But it sounds like you're doing much smaller chunks of stuff for multiple clients? I tend to dedicate myself to one client at a time and work more or less full time on one project. Serial monogamy one might call it... I'm not an employee because I work on a project basis and then leave with no fuss :) I'm definitely a contractor, are you more of a freelancer?