Project assumptions are those factors pertaining to a project that are taken for granted but cannot be guaranteed, such as staff availability, cooperation and punctuality or the proper functionality of necessary equipment. For the sake of planning a project, it is often necessary to make assumptions about factors such as these, but doing so does represent risk.
Sometimes, project assumptions will allow for poorly performing or absent staff by specifying only the minimum requirements for a project's success, such as four members of staff working at 25 percent of dedicated time. Further assumptions might then be made about the availability of additional staff if necessary.
Project assumptions are often discussed alongside constraints. Unlike assumptions, constraints are factors influencing a project that are not subject to change. They may be subdivided into the categories of business constraints and technical constraints.
Business constraints include restrictions of time, funding, resources and skills. Such factors are built into the existing organization of a business and must be taken into account when planning a project's outcome.
Technical constraints, meanwhile, are those imposed by available computer systems — hardware and software — and development or programming languages.
When identifying project assumptions and constraints, it is sensible to solicit suggestions from everybody involved, and to use these suggestions to formulate more realistic expectations.