Assume 8 hours * your hourly rate. You won't be programming productively for all eight hours probably, but that's normal. Be sure to point out that the day rate

Assume 8 hours * your hourly rate. You won't be programming productively for all eight hours probably, but that's normal. Be sure to point out that the day rate assures that you commit to focusing on them for the entire day, being available, and not working on other client work. This is the expectation of day rates for most clients: predictable scheduling and reachability.