A start date of a project is sometimes determined by the expected completion date. If a project is to be completed on a certain date and the project takes 90 days, then prior to the 90th day scheduled for completion, project management will determine the start date as to when everything will get underway. There are a number of start date scenarios: planned start date that of which would be the date a project is planned to start and project management would at that time have the workers scheduled to work on the appropriate date. There is the estimated start date, that of which the estimate is a general idea of the start date without a true commitment as to the actual ground breaking of the project. The scheduled start date is the date that all involved in the project have agreed upon and are planning according to the scheduled start date. With a scheduled start date, project management can actually determine when the equipment and personnel will need to be at the location.This date is usually a firm date, barring anything out of control of the participants. An early start date or a late start date is a time that the project was able to start before or after the initial start date time, due to a number of positive or negative reasons.
This term is defined in the 3rd and the 4th edition of the PMBOK.