Also, while I have never freelanced, I would define day rate as simply "not to exceed 8 hours". If they want to make it exactly 8 hours, fine, but that's where

Also, while I have never freelanced, I would define day rate as simply "not to exceed 8 hours". If they want to make it exactly 8 hours, fine, but that's where ethics comes in. For myself, if I'm mentally spent, and recognize I'll do more harm than good if I keep trying to code, I'm okay with simply keeping an eye on email and responding to them (rather than only responding to high importance ones/phone calls), and if any non-mental tasks are available, doing those (documentation, minor refactorings, additional test coverage, etc). EDIT: foz's comment x 100. Make it clear they're paying for exclusive rights to your time, not 8 hours of programming.