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

In Finish to Start relationship, Primavera calculate Early and Late date base on 2 process

  • Forward Pass (to calculate Early Start and Early Finish)


  • Backward Pass (to calculate Late Start and Late Finish)



In Backward Pass, the Late Start of successor (Activity C) will be the base to calculate Late Finish of predecessor (Activity A and B)

How about in Start to Start relationship.

In follow picture, the relationship between Activity B and Activity C is Start to Start.


There is no activity standing behind activity B.

So how can P6 calculate Late Finish for activity B.

In Start to Start relationship Primavera will do it in reverse direction. It will calculate Late Start first, then Late Finish = Late Start + Duration.

First Late Start of B = Late Start of C = 25/Sep

Then Late Finish of B = Late Start of B + Duration of B = 25/Sep +5 = 29/Sep

Bonus :

In Finish to Finish relationship, the finish dates will be calculated first.

  • In the forward pass, EF = predecessor's EF
  • In the backward pass, LF = successor's LF

Then, the start dates get calculated from finish dates.

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your example is only good if

your example is only good if there is not a project must finish by date or there is not a constraint on the last activity.

You did not mention where the backward pass begins. It begins at the project must finish by date or of there is a constraint date on the last activity. You need to mention the anchor point of where that backward pass begins 

You did not mention a very important part here is that is if there is not a  project must finish by daate or a constraint on the last activity then the Late Finish is equal to the latest calculated Early Finish date. IN your example day 25 that is WHY the backward pass beings here.

Also activities without successors are assigned a Late Finish equal to the latest calculated Early Finish date.  

Late Curve & Early Curve  

Late Curve & Early Curve     


Dear All, 

I am delveloping Early curve & Late curve as per my client request.

Can anyone help, is that Late curve should meet the early curve @ 100% or is that acceptable to meet after completing the early curve.

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