Start-to-Finish (SF) Logic

Start-to-Finish is the least-used relationship type in scheduling for a simple reason: it almost never accurately represents how work is actually sequenced. In an SF relationship, the successor cannot finish until the predecessor starts — meaning the successor is complete before its 'predecessor' in any logical sense. The only genuine use case most practitioners can cite is a just-in-time scenario: a new shift cannot finish (go home) until the replacement shift starts. In nearly all other cases where SF appears in a schedule, it is a modelling error — either the planner has confused the relationship direction, or they have applied SF to achieve a desired date outcome rather than to model a genuine dependency.

Because SF relationships are so rarely legitimate, they are a red flag in any schedule review. The DCMA 14-point assessment does not flag SF relationships directly, but any schedule quality review should examine SF relationships in detail. Ask the planner: what is the real-world reason Activity B cannot finish until Activity A starts? In most cases, the answer will reveal that the relationship should actually be FS or SS. SF relationships that cannot be clearly justified should be treated as errors and corrected.

The broader point that SF illustrates is that relationship types should always represent physical or contractual realities, not scheduling convenience. When planners use relationship types to force dates — applying SF to ensure an early finish, or using FS + negative lag to accelerate a successor beyond what the logic supports — they are building a schedule that looks right but does not model reality. A schedule that does not model reality cannot be used to forecast it. This is why relationship type audits are a standard part of any serious schedule quality review.