How Early and Late date are calculated in Start to Start relationship in Primavera P6

In a Finish-to-Start (FS) relationship, Primavera P6 calculates Early and Late dates using two main processes:

1. Forward Pass (Calculates Early Start and Early Finish)

• The Early Start (ES) and Early Finish (EF) of an activity are determined by the earliest possible time the activity can begin and end, based on its predecessor’s finish.

2. Backward Pass (Calculates Late Start and Late Finish)

• The Late Finish (LF) and Late Start (LS) are calculated by working backward from the project’s end date.
• In an FS relationship, the Late Start of the successor (e.g., Activity C) is used to calculate the Late Finish of the predecessor (e.g., Activities A and B).

What About Start-to-Start (SS) Relationships?

Let’s consider a scenario where Activity B and Activity C are linked with a Start-to-Start (SS) relationship.

In this case, there is no activity following Activity B, so how does Primavera P6 calculate the Late Finish for Activity B?

Here’s how it works:

• In an SS relationship, Primavera calculates Late Start first, then derives Late Finish using the activity’s duration.
• For example:
  • Late Start of B = Late Start of C = 25-Sep
  • Late Finish of B = Late Start of B + Duration of B = 25-Sep + 5 days = 29-Sep

Finish-to-Finish (FF) Relationships

In a Finish-to-Finish (FF) relationship:

• In the Forward Pass: EF = predecessor’s EF.
• In the Backward Pass: LF = successor’s LF.
• Then, the Start dates are calculated based on the Finish dates.