Why contractor schedules are optimistic by design
A schedule submitted by a contractor for client acceptance is not primarily a planning tool. It is a commercial document. It supports the contractor's claim for the programme-related component of their price. It establishes the baseline against which compensation events will be assessed. It tells the story the contractor wants the client to believe about how the project will be delivered. None of this means it is dishonest — most contractors produce schedules in good faith — but it does mean that the interests shaping the schedule are not aligned with the client's interest in an accurate picture of delivery risk.
The structural pressure toward optimism is real and pervasive. Tendering contractors who submit more realistic — and therefore longer — schedules lose work to competitors who show what clients want to see. Delivery contractors who revise their programme to show a realistic completion date later than contractually required must justify the revision commercially. Schedulers who want to show their management team a programme that looks achievable will round down durations and add float to the wrong places. The result is a population of contractor-submitted schedules in which optimism bias is the norm rather than the exception.
Client-side schedule assurance exists precisely to correct for this structural bias. Not by assuming the contractor is acting in bad faith, but by applying professional scepticism to the schedule and asking the questions that surface whether the plan is genuinely achievable or whether it represents a best-case scenario dressed up as a central estimate. The challenge is to do this in a way that is technically rigorous, commercially fair, and professionally constructive — asking hard questions without triggering defensiveness that shuts down the conversation.
The ten questions in this guide are the ones that consistently reveal the most about a schedule's credibility. They are structured to be asked in a face-to-face review meeting, but they apply equally to a written schedule review report. The framing matters: every question is an invitation to explain, not an accusation. The contractor who can answer them clearly and specifically has built a schedule worth accepting. The one who cannot has revealed where the programme needs more work.
The ten questions
Float. Ask where the float is and why. A schedule that shows planned completion exactly on the contractual completion date, with no float anywhere in the network, is a schedule that has been built to the contract deadline rather than to a realistic plan. Under NEC4, the difference between planned completion and contractual completion is commercially significant — it determines how compensation events are assessed. Under other contract forms it tells you whether the contractor has any schedule resilience at all. Ask the contractor to show you the activities with the highest total float and explain what they represent. Activities with unexplained high float usually indicate missing logic — the activity is not properly connected to the downstream work it should be driving.
Logic. Ask about the basis of the key dependencies. For the three or four most critical dependencies in the schedule — the ones where the relationship between activity A and activity B is what is driving the completion date — ask the contractor to explain why the relationship is structured the way it is. Experienced planners have immediate, specific answers: "we cannot start the mechanical installation until the structural steel frame is complete and inspected, because the mechanical supports hang from the secondary steelwork." When the answer is vague — "they're logically dependent" — or when the logic turns out to be a hard constraint rather than a genuine dependency, the schedule's reliability as a forecasting tool is reduced.
Resource loading. Ask which packages are resource-loaded and what the critical resource assumptions are. An unresourced schedule can be delivered on any imaginable timescale if you are willing to assume unlimited labour and plant. Ask specifically: at peak, how many of each key trade will be required? Has the contractor confirmed those resources are available? If the answer is "this schedule assumes we can get whatever labour we need, when we need it," the schedule is planning fiction. If the answer identifies specific subcontractors, confirmed resource commitments, and realistic productivity assumptions, the schedule is grounded in reality.
Critical path. Ask the contractor to walk you through the critical path — not from a printed report, but verbally, activity by activity. A planner who genuinely understands their programme can trace the critical path in conversation: "civils starts on this date and runs fourteen weeks to drainage completion; drainage completion is the predecessor for the services duct install, which takes six weeks; services duct completion is the predecessor for reinstatement, which runs to practical completion." If the planner cannot walk the critical path without looking at a report, or if the path they describe does not match the logic in the programme, the critical path has been generated by the software rather than designed by the planner.
Baseline versus current. Ask when the programme was last substantively updated and how it has been revised since the baseline. A programme that has been running for six months and whose logical structure is identical to the original tender programme has not been maintained — it has been status-updated, which is a much weaker activity. Ask specifically: what has changed since the last revision? What activities have been resequenced, what durations have been revised in light of actual productivity, what risks have been reflected in TRA adjustments? A programme that cannot answer these questions has been produced for reporting rather than for management.
Compensation events. Ask which compensation events have been notified and how they are reflected in the programme. Compensation events that have been agreed in principle but not yet formally assessed should appear in the programme — either as additional activities, as extended durations on affected activities, or as revised logic. If the contractor has a backlog of unassessed compensation events that are not in the programme, the programme is not an accurate picture of the project. Ask for the compensation event log alongside the programme and check whether the entries are consistent with each other.
Weather and access allowances. Ask how weather and access constraints are modelled. On a UK civil engineering programme, weather is a material schedule risk, particularly for earthworks, concrete pours, and highway works. The programme should show how weather windows have been incorporated — either as explicit non-working periods, as extended durations on weather-sensitive activities, or as TRAs. A programme that assumes twelve working months of weather-clear productivity on an exposed site in Scotland is not credible. Ask the contractor to identify the weather-sensitive activities and explain how weather risk is represented.
Commissioning logic. Ask about the logic connecting construction completion to handover. Commissioning sequences are frequently underplanned relative to the rest of the programme. The instinct is to plan construction in detail and leave commissioning as a block of time at the end. Ask to see the commissioning activities and their dependencies: which systems need to be commissioned before others can start? What are the regulatory or client hold points? What is the assumed duration for integrated testing and what is the basis for that assumption? The commissioning plan is where many infrastructure projects lose weeks and months that were never built into the programme.
Procurement lead times. Ask about the critical procurement items and how their lead times are modelled. Long-lead equipment — switchgear, transformers, specialist plant — should appear in the programme as explicit procurement activities with durations based on confirmed supplier quotes or tracked market data, not on wish-list assumptions. Ask the contractor to identify the three or four items with the longest procurement lead times and show where they sit in the programme and on the critical path. Equipment that is off the critical path but only marginally so, and that has a long lead time with limited supply chain flexibility, is a risk that should be in the risk register as well as the programme.
Handback and testing. Ask about the conditions required for handover and how they are reflected in the programme. Practical completion or handback requirements — snagging periods, O&M documentation, training, regulatory sign-offs, insurance compliance — often take significantly longer than planned. Ask the contractor what the handover conditions are under the contract and how the programme shows those conditions being met. A programme that ends with "practical completion" as a single milestone, with no activities representing the final inspection, documentation, and sign-off process, is a programme that has not been planned to the end of the project.
What to do with the answers
The ten questions produce one of three outcomes for each topic: a clear and credible answer that gives confidence in that aspect of the programme; a vague or incomplete answer that identifies an area for further investigation; or an answer that directly contradicts the schedule data and reveals a structural problem. The pattern of outcomes across the ten questions tells you more about the programme than any automated metric check.
A programme that answers eight or nine of the ten questions clearly and specifically, with the remaining one or two identified as areas where the contractor acknowledges the plan needs to be developed further, is a programme worth accepting with conditions. The conditions should be specific: "the commissioning logic needs to be developed to activity level before the next revision" or "the weather-sensitive activities should have explicit TRAs added." Accept the programme against the evidence that exists, not against a theoretical ideal, and set clear expectations for what the next revision needs to contain.
A programme where four or five questions receive vague or incomplete answers is a programme that is not ready to be accepted. The appropriate response is a written schedule review report that identifies the specific deficiencies, explains why each one matters, and sets out what the contractor needs to address before resubmission. This report is not a rejection — it is a specification for what a credible programme looks like on this particular project. Framing it as guidance rather than criticism ("we need the commissioning sequence developed to this level of detail" rather than "the commissioning sequence is inadequate") maintains the collaborative tone that makes the subsequent revision more productive.
A programme where the answers to the critical path, logic, or compensation event questions directly contradict the schedule data is a programme that has been produced for presentation rather than for management. This is the most difficult conversation to have without triggering defensiveness, because it implies that the schedule has been constructed to tell a story rather than to model the work. The most effective approach is to be specific about the contradiction rather than making a general observation about quality: "The programme shows a finish-to-start dependency between the structural frame and the mechanical installation, but when I asked about the commissioning logic you described the two packages running concurrently. Can you help me understand how those two things are consistent?" Specific contradictions invite specific explanations; general quality observations invite general defensiveness.
The broader principle is that schedule assurance is a conversation, not a verdict. The objective is a programme that accurately represents how the project will be delivered, that the contractor is committed to, and that the client can use to make decisions about resources, risk, and commercial exposure. A programme accepted after a rigorous but constructive challenge is more valuable than one waved through without scrutiny — because it is more likely to be a genuine plan rather than a presentation. Contractors who are asked hard questions and answer them well produce better programmes next time. Contractors who are never asked them do not.