Starttofinish

Start-to-finish, often abbreviated SF, is a type of dependency used in project scheduling. It states that the finish of the successor task cannot occur before the start of the predecessor task. In other words, B must finish after A has started, potentially with a lag. SF is one of the four common dependency types in CPM/PERT, alongside finish-to-start (FS), start-to-start (SS), and finish-to-finish (FF). It is relatively rare in practice because it can constrain scheduling and complicate planning.

In practice, SF models constraints where a downstream activity depends on the initiation of an upstream activity rather than its completion. For example, a final regulatory review (B) may be allowed to conclude only after a product development phase (A) has begun. Similarly, some release or validation processes require that certain checks cannot be completed until the initial design work has started. The specific lag between the start of A and the finish of B can be adjusted to reflect real-world timing.

Software tools used for project scheduling typically support SF relationships and allow setting optional lags. Because an SF constraint ties B’s completion to A’s start, it can reduce scheduling flexibility and extend the project timeline if not used carefully. Practitioners consider SF when a project situation genuinely ties a finish to the initiation of another activity, and they assess its impact on risk and schedule robustness.