We are a contracting company (not construction, more field data acquisition and technical services, but the situation still applies) that generally charge Lump Sum. Our clients almost always also want a "daily rate" stated as well even though we are biding as Lump Sum. On longer jobs (over a week or two) it sometimes becomes apparent that we can complete the work in a shorter amount of time, maybe a day or two earlier, usually due to favourable conditions. We are then faced with a client that is expecting us to charge less because we finished early. This forces us into an unfair situation where we are either expected to make less money for doing our job more efficiently or make sure we use up the whole time we anticipated. In these situations, we generally opt to acquire slower so that we will take the entire anticipated time in the end. Is this a reasonable thing to do? How can we change our contracts to protect our interests if we might end up finishing early? Thanks!