Testing the schedule: which late activities would hurt most
At the monthly review of a four-storey apartment building, the owner's representative asks which activities could still push occupancy past 1 April, when the tenants move in. The schedule has 380 activities, 41 of them with zero float. The project manager can name the critical path, but not which activities would do the most damage if they ran late.
Find them by testing: copy the schedule, delay one activity at a time by a realistic amount, record how far the finish moves and what else the delay pushes, and protect the few that do the most damage. Float shows how much room an activity has, not how likely it is to lose more than that. The US Government Accountability Office calls activities whose float is close to that of the critical path near-critical, because they can quickly become critical if a delay uses up their small float. Its schedule guide also describes a statistical schedule risk analysis that predicts the confidence of meeting the completion date and identifies the high-priority risks; a what-if test is a simpler check you can run by hand.
- Work on a copy of the latest update, never on the schedule of record.
- Pick 10 to 15 candidates with real uncertainty, critical or not: utility and authority dates, long-lead deliveries, inspections, owner decisions, weather-exposed work.
- Give each a realistic delay from someone who knows, such as the supplier's recent record, and note where the number came from.
- Delay one, recalculate, record, undo: the new finish, the milestones that move, and anything pushed into winter or past a lease date.
- Rank by damage: days of finish movement times the daily cost of running late, plus one-off costs.
- Protect the top three to five — order earlier, book early, add a crew or write a plan B — and repeat the test at each major update.
Common mistakes
- Testing only zero-float activities and missing the near-critical ones.
- Using the same delay for every activity.
- Ranking by days alone and missing a push into winter or past a lease date.
- Testing on the live schedule and forgetting to undo it.
Checklist
Record for each test
- The activity, the delay tested and where the number came from
- The new finish date and the milestones that moved
- Work pushed into winter, a shutdown window or a lease date
- Days times the daily cost, plus one-off costs
- The float left on its chain
- The protection chosen, with an owner and a date
Check your understanding
A critical activity's supplier is never more than a day late. A near-critical activity with 8 days of float depends on one that is often four weeks late. Which do you protect first?
