Windows analysis is a delay analysis method that splits the project into periods (windows), usually between schedule updates, and measures how far the forecast completion date moved in each one, what drove the critical path, and who caused it. The two most common forms are contemporaneous period analysis, which reads the project’s own updates as they were, and time-slice windows analysis, which also models each delay event at the start of the window.
Below: how windows analysis works, the three main variants, a step-by-step worked example with a windows chart, and what owners should check. For the full menu of delay methods, see our delay analysis methods guide.
How windows analysis works
A delay claim asks two questions: how late is the project, and whose fault is it? Windows analysis answers both one slice at a time. Instead of looking at the whole job at once, the analyst takes each window, compares the schedule at its start and end, and records:
- how many days the forecast completion moved (critical delay or gain);
- which activities were on the critical path, and whether it shifted;
- which events drove the movement, and who was responsible for them.
Because each window is judged on what the schedule showed at the time, the method captures changes in the critical path, mitigation and acceleration that a single before-and-after comparison misses.
Contemporaneous period analysis vs time-slice windows analysis
All windows methods share that structure. They differ in what they compare within each window. The SCL Delay and Disruption Protocol (2nd edition, 2017) names two windows methods, and AACE International’s RP 29R-03 gives the same ideas a formal taxonomy.
| Contemporaneous period analysis | Time-slice windows analysis | As-planned vs as-built windows | |
|---|---|---|---|
| How it works | Compares consecutive schedule updates as they were; measures the change in forecast completion and the critical path in each window | Adds a forward-looking model of each delay event at the start of the window, then checks it against the update at the end | Compares the planned and as-built progress of the critical activities within each window |
| Needs | Reliable, logic-linked updates | Updates plus delay fragnets | Baseline plus good as-built data |
| AACE / SCL name | Closest match: MIP 3.3, observational, dynamic, contemporaneous as-is | Hybrid of MIP 3.7 and MIP 3.3; SCL: time slice windows analysis | SCL: as-planned vs as-built windows analysis |
| Best when | Updates were kept well during the job | Cause and effect must be shown event by event | Updates are weak but as-built records are good |
In practice, contemporaneous period analysis is often the most persuasive when the contractor kept good monthly updates, because it relies on records both parties saw at the time. Time-slice analysis adds a modelled view of each event, which helps separate owner and contractor delay, and concurrency, within the same window.
Worked example: four monthly windows
Take a hypothetical project with a baseline completion date and four monthly updates. The analyst reads the forecast completion from each update:
View the data
| Update | Forecast completion vs baseline |
|---|---|
| Baseline | +0 days |
| End Jan | +10 days |
| End Feb | +16 days |
| End Mar | +12 days |
| End Apr | +24 days |
Then, window by window:
- Window 1 (January): forecast completion moves 10 days later. The critical path ran through design information the owner issued late. Owner-caused: 10 days.
- Window 2 (February): a further 6 days. The critical path shifted to structural steel, which the contractor delivered late. Contractor-caused: 6 days.
- Window 3 (March): the forecast improves by 4 days after the contractor resequenced the work. Mitigation: 4 days recovered.
- Window 4 (April): 12 days later after the owner instructed added scope on the critical path. Owner-caused: 12 days.
View the data
| Window | Critical delay | Cause | Responsibility |
|---|---|---|---|
| Window 1 (Jan) | +10 days | Late design information | Owner-caused |
| Window 2 (Feb) | +6 days | Late structural steel | Contractor-caused |
| Window 3 (Mar) | -4 days | Contractor resequencing | Mitigation (gain) |
| Window 4 (Apr) | +12 days | Added scope instructed | Owner-caused |
| Total | +24 days | Owner 22, contractor 6, mitigation −4 | |
The result: 24 days of net delay. The owner is responsible for 22 days and the contractor for 6, with 4 days recovered. Whether the contractor gets time, money or both for the owner’s 22 days depends on the contract, on float, and on any concurrency inside each window. Our posts on float ownership and concurrent delay cover those questions.
Note what the windows view shows that a single comparison wouldn’t: the critical path changed twice, and the contractor’s delay in February was partly offset by its own recovery in March.
What owners should check in a windows analysis
- The updates themselves. Windows analysis is only as good as the schedules it reads. Check that each update has sound logic and a reliable data date. Our schedule review checklist helps.
- How the windows were chosen. Windows can follow the update dates or the moments the critical path changed. Unusual window boundaries can shift delay between parties.
- Consistency. The same rules should apply in every window, for both parties’ delays.
- Mitigation and gains. Recovered days belong in the analysis, not just the losses.
- The link to entitlement. Days of delay are not days of compensation until the contract terms are applied. See our guide to evaluating a delay claim.
FAQ
What is windows analysis?
Windows analysis is a delay analysis method that divides the project into periods, or windows, usually between schedule updates. In each window it measures how much the forecast completion date moved, what drove the critical path and who was responsible, then adds the windows up.
What is contemporaneous period analysis?
Contemporaneous period analysis is a form of windows analysis that uses the schedule updates prepared during the project, as they were. It compares consecutive updates to measure critical delay and identify the critical path in each period. The closest match in AACE RP 29R-03 is the observational, dynamic, contemporaneous as-is method (MIP 3.3).
What is time slice windows analysis?
Time slice windows analysis is a hybrid method named in the SCL Delay and Disruption Protocol. For each window it models the expected impact of delay events at the start of the window, then compares that with the schedule update at the end of the window to show actual delay, mitigation and concurrency.
What is planned vs as-built analysis?
As-planned vs as-built analysis compares the baseline schedule with what actually happened. The SCL Protocol describes a windows version that makes the comparison period by period, which suits projects with good as-built records but weak schedule updates.
The bottom line
Windows analysis turns a delay argument into a sequence of smaller, checkable questions. Owners who keep good monthly updates during the job make that analysis faster, cheaper and harder to dispute. The time to invest in schedule quality is before the claim arrives.
Facing a delay claim, or want your updates claim-ready? See our owner tools or book a 30-minute call.
Sources: HKA, Time Slice in Window Analysis (Hybrid Delay Analysis); Addleshaw Goddard, The SCL Delay and Disruption Protocol 2nd edition; RP 29R-03 taxonomy and method selection (study guide); AACE International, Recommended Practice 29R-03, Forensic Schedule Analysis. The worked example is hypothetical. This article is general information, not legal advice.