A constraint can be legitimate. A contractual milestone, a possession window or a plant delivery the team does not control may need a date held in the file. The failure starts when the constraint is used instead of logic: predecessors are missing, the critical path is forced, and float looks healthy because the software is not allowed to tell the truth.
Constraints vs logic is not a software debate. It is a delivery debate. Logic explains how the work gets done. A constraint only states when someone wants it done. When the second replaces the first, delay is already in the file—it is just not visible yet.
What a constraint is supposed to do
A constraint overlays a date rule on an activity: start-on, finish-on, start-no-earlier-than, mandatory finish, and the rest. Used sparingly, it records an external boundary the network cannot invent. Used generously, it becomes a way to protect a board date without building the path that earns it.
Primavera P6 and MS Project will calculate around whatever constraints you give them. They will not refuse a soft process. Discipline is a planner rule, not a button.
How constraints hide delay
- A mandatory finish holds a milestone while open-ended predecessors still float underneath.
- Start-on dates force a trade to “begin” with no access, design or materials predecessor.
- As-late-as-possible and similar settings push work until float looks artificial.
- Multiple hard constraints create a path that cannot respond when remaining duration grows.
- Updates shorten remaining duration to keep the constrained date, instead of showing the slip.
Each practice can look tidy in a Gantt. Together they produce a finish date that no longer comes from the work.
| Constraint habit | What the file shows | What is hidden |
|---|---|---|
| Mandatory finish on handover | Date held | Missing commissioning logic |
| Start-on without access | Trade “starts on time” | Blocked predecessor |
| Constraint instead of FS link | Clean bars | Broken network |
| Many SNET dates | Artificial float map | True driver unclear |
| Duration cut to protect constraint | SPI comfort | Delay absorbed into optimism |
Logic first, constraint second
Build the network so predecessors explain the date. Only then add a constraint that records a real external boundary—and write why it exists. If the constraint is removed in a health check and the finish collapses, the constraint was carrying the schedule, not the work.
A practical test before every baseline or update
- List every hard and soft constraint and the reason for each.
- Remove or convert unjustified hard constraints in a copy and recalculate.
- Check whether the driving path still walks without open ends.
- Confirm remaining duration was not shortened only to protect a constrained date.
- Put any retained constraint in the narrative so directors know it is a boundary, not a miracle.
What directors should ask
Ask how many hard constraints are in the file. Ask which finish dates are calculated and which are forced. Ask what happens to the critical path if those constraints are cleared. If the room cannot answer, do not argue about float yet. Fix the network.
Constraints still belong—when they are honest
A possession that the railway owns, a court date, a grid outage window, a landlord access rule: those are real. Record them. Do not use them to paper over missing design release, incomplete procurement or unfinished punch lists.
EVM Solutions reviews schedule logic and constraint use as part of planning and project controls. If your finish date only holds because of hard constraints, send the current P6 or Project file and the constraint list. The hidden delay is usually visible as soon as the network is allowed to speak.
