How do you calculate project float manually vs using a tool

Question

When calculating float, do you prefer doing it manually (with forward/backward pass) or relying on scheduling tools? I’d like to understand both for training purposes.

Answer 1

Project float (or slack) refers to the amount of time a work can be delayed without compromising the overall project timeline. Float is an important concept for project planning and resource management. Here's how you can compute project float manually or with a tool:

• Manual Calculation of Float:
  • Total Float Formula - Each task in a project's float is computed as: 

       Total Float = Late Start (LS) - Early Start (ES) or Total Float = Late Finish (LF) - Early Finish (EF)

• The Late Start and Early Start timings are the latest and earliest times a work can begin without disrupting the overall project timeline. Similarly, Late Finish and Early Finish denote the appropriate finish times.
• Subtracting the early and late start/finish times yields the float for that task.
• Using A Tool:
  • Project Management Software - Microsoft Project, Primavera P6, and even JIRA all provide automated float calculations based on the project's Critical Path Method (CPM). By inputting task durations, dependencies, and limitations, these tools may calculate and update the float for each task in real time.
  • Using a tool is faster and more precise, particularly for large projects with several tasks and dependencies. Manual computations, on the other hand, can be useful for smaller tasks or to double-check tool outputs.