How to Calculate Total Slack

Written by emily fisher
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How to Calculate Total Slack
Many project managers utilise total slack to assist with a successful on-time project completion. (builder and the project manager image by Dmitri MIkitenko from

Total Slack (TS) is a term used by project management professionals. This term describes the additional amount of time that can be lost on a project without delaying the project due date. Conversely, negative slack provides the project manager the amount of time they need to adjust other tasks to make up for the deficit. It is important to know the total slack to assist with incidental delays that might arise. Calculating total slack is not difficult.

Skill level:


  1. 1

    Determine the latest number of days completion date for your project. This is called late finish (LF).

  2. 2

    Determine the early start date for your project (ES). For example, if this activity is the first activity in your project, your early start is 1. If this is activity 2 and activity 1 completed with an early finish of day 3, your early start for this activity will be 3.

  3. 3

    Begin calculation using the formula for calculating total slack. This formula is TS = LF - ES - Duration. For example if your late completion is 10 days, early start is 1, and your duration is 5, your total slack is 4.

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