Time Impact Analysis in Windows (TIA) is recognised as one of the most credible techniques for analysing construction delays according to AACEI MIP3.7 Recommended practice 29R-03. This type of analysis was used to produce a concurrency analysis to prove contractor entitlement to prolongation costs. The critical path was investigated in a similar way to the Time Slice method. After investigation, fragnets were built using supporting documentation. The selection of the updated programme to be impacted was made based upon the start date of the delay fragnet. The selected updates created the window periods, therefore this method breaks the project into discrete time increments (Windows) and examines the effects of the delays attributable to each project participant as those delays occur. The TIA in Windows contains elements of retrospective analysis as the project programme is reviewed in a series of ‘snapshots’ or ‘time slices.’ The analysis also contains a prospective analysis as the delays identified are swapped for an element of ‘prospective’ modelling. The analysis therefore combines a retrospective and prospective view and can be easily used to provide clear demonstration and calculation of concurrency and mitigation. The concurrency analysis using the TIA in Windows method has successfully led to the granting of prolongation costs to contractors.