Finish-to-Start (FS) Logic

Finish-to-Start is the default relationship type in most scheduling tools and by far the most common in practice. Activity B cannot start until Activity A finishes. The DCMA 14-point assessment expects more than 90% of all relationships to be Finish-to-Start because overuse of other relationship types — particularly when combined with lags — can make a schedule harder to analyse and more prone to modelling errors. FS relationships drive the classical Critical Path Method calculation: each forward pass step applies a FS relationship to move from the finish of one activity to the start of the next.

The prevalence of FS logic does not mean it is always the right choice — it means it should be the default and departures from it should be deliberate and documented. FS relationships combined with lags are sometimes used as a shorthand for more complex overlapping logic that would more honestly be represented by Start-to-Start or Finish-to-Finish relationships. When a reviewer sees a long string of FS relationships with large lags, that is often a sign that the planner has not thought carefully about how the work actually overlaps.

On NEC contracts, the logic of the Accepted Programme is scrutinised closely because it drives compensation event assessments. If a programme shows a FS relationship between two activities that in reality are partially overlapping, a delay to the predecessor will be assessed as delaying the successor by the full duration of the predecessor — which may not be what actually happens on site. Getting the relationship type right at the outset is not an academic exercise; it directly affects how compensation events are valued and how float is shared between the parties.