Data Type Duration (duration field: A type of field whose content is expressed as a duration of time. Examples include the Work, Duration, and Delay fields. A duration field includes the duration unit, such as hour, day, or week.)
Entry Type Calculated (calculated field: A field in which the value is determined by Project based on information in other fields. Project may recalculate the value automatically or when you specify, depending on your choice of calculation settings.)
Description The Total Slack field contains the amount of time a task's finish date can be delayed without delaying the project's finish date.
How Calculated Microsoft Office Project bases its calculations of total slack on comparisons of the dates in the Early Start, Early Finish, Late Start, and Late Finish fields for the task, which in turn take into account the dates for any successor tasks. Total slack is calculated as the smaller value of the Late Finish minus the Early Finish field, and the Late Start minus the Early Start field.
Best Uses Use the Total Slack field to determine whether the task has any time available for a delay. This can be useful if a resource needs more time on a task, or if you want to assign a resource to another task. You can also use the Total Slack field to determine how to recover a schedule that's slipping.
Example You have received suggestions from management about some additional tasks to add to the project. You have agreed to review the schedule to see whether there is any slack to accommodate any new tasks. You add the Total Slack field to the task sheet and look for sizable positive numbers, which indicate there is some extra time available in the schedule.
Remarks Total slack can be positive or negative. If total slack is a positive number, it indicates the amount of time that the task can be delayed without delaying the project finish date. If total slack is a negative number, it indicates the amount of time that must be saved so that the project finish date is not delayed. Negative slack indicates that there is not enough time scheduled for the task and is usually caused by constraint dates.
The behavior of total slack can differ depending on the link type. For example, if you're working with a Start-to-Start task relationship, the total slack can change when you enter progress on the predecessor task. With progress entered on the predecessor task, the start date of the successor task is now known and becomes part of the total slack calculation.