When you open a new project file in Microsoft Project, you can enter your project’s start or finish date, but not both. It’s most common, and recommended, that you enter only your project’s start date and let Microsoft Project calculate the finish date after you have entered and scheduled tasks (see Chapter 10, "Evaluating Your Schedule and Analyzing Tradeoffs"). If your project must absolutely be finished by a certain date, then enter only the project’s finish date.
To change a project start or finish date