Primavera P6: Schedule Options – Calculate start-to-start lag from

In Primavera P6 Schedule Options, there are 2 options for “Calculate start-to-start lag from”.

The purpose of these option is described below.

We have a simple project:

The schedule option in this article is applicable when a start-to-start relationship exists and the predecessor starts out of sequence.

The activity B started out of sequence (it started before activity A finish) as picture below:

The start date of activity C will be determined depending on which option is selected in Schedule Options:

Choose “Early Start” when the successor’s start depends on the amount of work that the predecessor activity accomplishes. The expired lag is calculated as the number of workperiods between the actual start and the data date. The successor’s start date is the predecessor’s internal early start plus any remaining lag.
The expired lag of activity B is 1 day (Tuesday).
The remaining lag of activity C is 1 day ( 2 – 1 = 1) which will be consumed on Friday so the start date of activity C is Saturday.

Choose “Actual Start” when you want the successor’s start to depend on the time elapsed from the predecessor’s actual start (regardless of the amount of work that has been accomplished in the predecessor activity). The successor’s start date is the data date plus any remaining lag.
The lag duration is calculated from actual start date of activity B. The lag is consumed on Tuesday and Wednesday. Therefore, start date of activity C is Thursday.