Forward & Backward Passes

Calculating the forward and backward passes in a project schedule is an essential step in project management. The forward pass is used to calculate the early start and finish dates for each activity in the project, while the backward pass is used to calculate the late start and finish dates for each activity. Both the forward and backward passes are important for determining the critical path of a project and for identifying potential areas of risk.

The Project Management Institute (PMI) provides guidelines for calculating the forward and backward passes in a project schedule. According to PMI, the forward pass is calculated by starting with the project's start date and working through each activity in the project schedule. The early start date for each activity is determined by the earliest possible finish date of the preceding activity. The early finish date for each activity is then calculated by adding the duration of the activity to the early start date.

Once the early start and finish dates have been determined for each activity, the backward pass can be calculated. The backward pass is used to determine the latest possible start and finish dates for each activity. According to PMI, this is done by starting with the project's finish date and working backwards through the project schedule. The late finish date for each activity is determined by the latest possible start date of the succeeding activity. The late start date for each activity is then calculated by subtracting the duration of the activity from the late finish date.

The critical path of a project is the sequence of activities that must be completed on time in order for the project to be completed on schedule. The critical path is determined by identifying the activities with the earliest and latest start and finish dates. The activities that have the same early and late start and finish dates are considered to be on the critical path. Any delay in the completion of an activity on the critical path will result in a delay in the overall completion of the project.

The American Association of Cost Engineers International (AACEI) also provides guidelines for calculating the forward and backward passes in a project schedule. According to AACEI, the forward pass is calculated by working through each activity in the project schedule and determining the earliest start and finish dates based on the preceding activities. The backward pass is calculated by working through each activity in the project schedule and determining the latest start and finish dates based on the succeeding activities.

AACEI also notes that the critical path can be identified by comparing the early and late start and finish dates for each activity. Activities that have the same early and late start and finish dates are considered to be on the critical path. AACEI also emphasizes the importance of identifying potential areas of risk by identifying activities that have a limited amount of float or that are critical to the completion of the project.

In conclusion, calculating the forward and backward passes in a project schedule is an essential step in project management. The forward pass is used to determine the earliest start and finish dates for each activity, while the backward pass is used to determine the latest start and finish dates. Both the forward and backward passes are important for identifying the critical path of a project and for identifying potential areas of risk. The guidelines provided by PMI and AACEI can be used to ensure that the forward and backward passes are calculated correctly and that the critical path and potential areas of risk are identified.