The goal is 100%. Electrical distribution systems consultant with over 25 years experience. I do not normally manage people, but sometimes have a support staff and work independently as a consultant to other organizations. The philosophy started out that anything preventing me from leaving the office was billable.
Reality is that I work 10 hours per day to allow non-billable marketing and technical updates, and often work one day per weekend to make deadlines. Much of how much I bill depends on the individual contract allowances and including the 'extra time' I put in to run the business I bill from 100% to as low as about 72%. I enjoy what I am doing, and have made concessions (extra hours) to keep the family budget okay.