• Sometimes known as Critical Path Analysis
  • CPA is a project analysis and planning method that allows a project to be completed in the shortest possible time

Information needed for CPA

  • A list of all activities required to complete the project
  • The time (duration) that each activity will take to completion
  • The dependencies between the activities (eg, activity D cannot be completed until both activities B and C are done.)

What is the Critical Path?

  • The sequence of a project activities which add up to the longest overall duration. The critical path determines the shortest time possible to complete the project.

Why is the Critical Path so important?

  • Any delay of an activity on the critical path directly impacts the planned project completion date (ie, there is no float on the critical path)

EST - Earliest start time LFT - Latest finish time

Calculating ESTs

  • The first node will always have an EST of 0
  • ESTS are calculated left to right
  • Add the duration of the activity to the EST of the previous node
  • If more than one activity leads to a node, the highest figure becomes the new EST

Calculating LFTs

  • Give the last node of the project an LFT equal to the EST
  • Work backwards from right to left
  • Subtract the duration of the activity from the LFT

Right to left is lower, left to right is higher

Calculating the float

  • The float is the duration an activity can be extended or postponed so that the the project still finished within the minimum time Calculated as:
  • LFT less Activity Duration less EST

Identifying the Critical Path

  • Activities with a float of 0 cannot be delayed without delaying the entire project
  • Such activities represent the “critical path”

Use of critical path analysis

  • Estimate and minimise project time
  • Support project costing and evaluation
  • Plan and organise resources
  • Prioritise tasks
  • Help provide direction


  • Reduces risks and costs of complex projects
  • Encourages careful assessment of the requirements of each activity in the project
  • Help spot which activities have some slack or float and could transfer resources
  • A decision-making and planning tool
  • Provides managers with a useful overview
  • Links well with other aspects of planning


  • Reliability of CPA largely based on accurate estimates and assumptions made
  • CPA does not guarantee the success of a project
  • Resources may not be as flexible as management hope when calculating network float
  • Too many activities may make the network diagram too complicated. Activities themselves might have to be broken down into mini-projects.