Calculating Float and Early/late Start Times in Critical Path Analysis: Step-by-step Guide

Critical Path Analysis is a project management technique used to identify the sequence of activities that determine the overall project duration. Calculating float and early/late start times helps in understanding schedule flexibility and managing delays effectively.

Understanding Float in Project Scheduling

Float, also known as slack, is the amount of time an activity can be delayed without affecting the project’s overall completion date. It is essential for identifying which activities have scheduling flexibility and which are critical.

Calculating Early Start and Early Finish Times

Early start (ES) is the earliest time an activity can begin, considering the completion of its predecessors. Early finish (EF) is calculated by adding the activity duration to its early start.

To determine ES and EF:

Start with activities that have no predecessors, setting their ES to zero.
For subsequent activities, set ES to the maximum EF of all immediate predecessors.
Calculate EF by adding the activity duration to ES.

Calculating Late Start and Late Finish Times

Late finish (LF) is the latest time an activity can end without delaying the project. Late start (LS) is determined by subtracting the activity duration from its late finish.

To find LF and LS:

Begin with the project’s final activity, setting its LF equal to its EF.
For preceding activities, set LF to the minimum LS of all immediate successors.
Calculate LS by subtracting the activity duration from LF.