The estimate to complete is an input output mechanism that is used to determine y the project team and the project leaders what will be the expected or anticipated costs that are going to be needed to ultimately complete the entirety of the remainder of work on the project or on a particular phase of that project such as a particular schedule activity or a specific work breakdown structure component. The estimate to complete is something that can and should be derived as quickly and as early in the process and/or life cycle of the project as it most adequately and effectively will help the team budget accordingly. However, if the estimate is done early and there is a need at some point to modify it, this can be done once or if needed even more than once during the life cycle of the specific project in question. Please also see earned value technique and estimate at completion for more information.
This term is defined in the 3rd and the 4th edition of the PMBOK.