Forensic delay analysis: Modeled or planned v. as-built – in periods

28th July 2018

A forensic delay analysis should at least produce the following:

  • Identification of activities that actually caused delay to the critical path; and
  • Quantification of critical delay caused by each activity.


In theory, the “actual” amount of critical delay caused by an activity should be an objective endeavor. However, as most of us are aware, consultants on opposing sides of a dispute will usually (always) arrive at vastly different conclusions regarding the activities that caused delay and the amount of delay caused by each. Part of the difference is often in the selection of a method of analysis.

A consultant can use any methodology when presenting a forensic delay analysis, but some are more robust than others. Understanding this is key to evaluating delay analyses prepared by others and calling out their ‘errors’.

For purposes of this narrative, I will focus on the most widely used methods of delay analysis:

  1. Impacted As-Planned
  2. Time Impact Analysis
  3. Planned v. As-Built.

In order to avoid confusion regarding the nomenclature this narrative defines the three methodologies as follows:

1. Impacted As-Planned (IAP)

An analysis that uses the IAP methodology consists of inserting “fragnets” in the planned project schedule (baseline) to measure the change to the completion date.

A fragnet is a network of one or more activities that represents a change or other impact that was not part of the planned project schedule.

The planned project schedule, often referred to as the baseline schedule, is the schedule that includes all the work of the original contract (without change orders). For the analysis, it is preferable to use an approved baseline schedule, and if not formally approved, the schedule that was used by the parties contemporaneously.

This method of analysis concludes that if after inserting the fragnet (or multiple fragnets inserted in chronological order) into the baseline schedule the completion date is delayed (can only be later), then the cause of that delay was the change represented by the fragnet(s).

2. Time Impact Analysis (TIA)

The principal difference between the TIA and the IAP is that in the TIA, the fragnet is inserted in a project schedule update – preferably one closest to the actual date of the change represented by the fragnet. As in the case of the IAP, if the project completion date changes (becomes later) after insertion of the fragnet, then it is concluded that the change or impact represented by the fragnet was the cause of the delay.

A very simple example of the application of the TIA/IAP is as follows:


In this example above: the baseline/update schedule has a critical path through activities A, B and D and a project duration of 20 days.

Fragent Insertion: Fragnet X (3 days) represents a change that was performed after Activity B and before Activity D.

Based on this simple example, the completion date has been delayed 3 days. The cause of the delay is the change or impact represented by Fragnet X.

3. Planned v. As-Built – in Periods (PAB)

The PAB method of analysis compares the planned performance to the actual or as-built performance evaluating each impact to the critical path (critical path being a dynamic/evolving condition) in a chronological and cumulative manner. Again, it is preferable to start with an approved schedule, but if a formally approved schedule is not available, then the plan used for construction should be used. The as-built data can usually be obtained by any combination of schedule updates, daily/weekly reports or correspondence.

When there are significant changes in the planned performance, the analysis should be divided into periods (often referred to as windows) such that the actual performance is compared to the contemporaneous plan. Generally each period will commence with an approved schedule update (if not approved then one that was used for construction) that includes the changed plan.

There are variations of the methods described above.


RP 29R-03 separates the retrospective delay analysis methodologies into two categories: Observational and Modeled (Additive and Subtractive). The Observational methods are variations of the PAB and the Modeled Additive methods are variations of the IAP and the TIA. The Modeled Subtractive method is not used as frequently as the methods addressed herein.

The RP 29R-03 does not recommend the use of one method over another, it describes the different methods.

A consultant can use any methodology when presenting a forensic delay analysis, but some are more robust than others. Understanding this Is key to evaluating delay analyses prepared by others and calling out their 'errors'.”
John H. McTyre, Partner,, HKA