This recommended practice (RP) of AACE International introduces the concepts of trending and forecasting as applied in CPM planning and scheduling. This RP presents practices which utilize information from the measured progress and performance of an ongoing project. This should be distinguished from other practices that draw upon historical information from similar past projects in the preparation of the original baseline plan. As practitioners follow the unfolding of the project, they may identify trends that vary from the initial or subsequent baseline schedules. Potential trends should be communicated to project team members but show restraint in revising the logic network as a response to the identified trends. This RP suggests that a potential trend must be reviewed and assessed, but not to automatically override, the original durations and sequences prepared by the initial project team for reasons discussed herein.

This RP is intended to provide guidelines (i.e., not a standard) for:

• Determining the existence of trends within CPM update data (measured progress) to date for a specified project.
• Determining and quantifying a trend or trends based upon such measured past performance.
• Use of such trend data to forecast future variation from an initial schedule or previous forecast.

CPM theory is built on the concept of forecasting activity and project completions. An RP on forecasting and trending must deal with the ability of CPM analysis to forecast or estimate the completion and the timing of discrete activities within a project. A traditional CPM schedule is a forecast because it is based upon the project management team’s initially selected means and methods (including selection of crews, equipment and other resources), scope of activities, optional sequences for activities, estimates of productivity, activity duration, calendar, and external considerations. These parameters are generally static and not subject to modification except pursuant to a revision or re-baselining of the initial (or previous) CPM logic plan. Therefore, CPM schedule updates are normally limited to addition of information such as actual start and finish dates, percent completeness and remaining duration of work in progress; these updates do not extend to modifying any other data of the initial (or previously modified or re-baselined) CPM logic plan. Changes in the CPM schedule for reasons including scope growth generally require a change in baseline. If not referenced appropriately, the trends, impacts, and forecasts may not be accurate against an appropriate reference point.