Home >

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

Meet the author:

Tal Levanon – Founder and partner in “Tal Levanon – HCP Ltd”, an expert project scheduling consultant and creator of the Hidden Critical Paths (HCP).

326992794_1264513354417332_8313151096923876505_n.jpg

There are situations in which milestones are linked to other activities in a project using SS (Start-to-Start) or FF (Finish-to-Finish) links.

Since the duration of a milestone is zero (that’s the definition of a milestone), there is no significance to SS or FF links with a milestone. Instead, we should use FS (Finish-to-Start) links.

For example, when a milestone triggers the start of other tasks, we place it before those activities and link them using an FS link (rather than SS, even though, on the surface, they may appear the same):

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

Conversely, when a milestone signifies the completion of other tasks, we place it after those activities and link them using an FS link (not FF, even though they may appear the same):

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

However, there are peculiar situations that arise in schedule Gantt charts, and let’s discuss them now:

Special Case (i): The Successor is a Milestone with a 'Start-to-Start’ (SS) Link

The scenario looks like this in the Gantt chart:

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules
In this case, we have Task/Activity I that starts on Wednesday, as shown in the example. We also have a milestone that is the successor (i.e., comes after the activity) in an SS link.
 
In other words, the milestone describes the start of an activity, not its end.

This situation is interesting, if not downright peculiar:

What’s the story behind defining a milestone that doesn’t trigger any activity but merely created from the start of one?

Determining the start of an activity can be quite challenging. Let’s take the example of ‘casting a wall’:
 
1. Does the activity start when the previous activity finishes? Is it still true, even if nothing is happening in the new activity? For instance, if the foundation is poured, is that when wall casting begins? (Answer: Not sure.)
 
2. Does the activity start when execution begins? For example, does wall casting start when the formwork is set up, or perhaps only when the ironwork is performed, or only when the actual casting occurs?
 
3. Maybe the activity starts when we organize for its execution – such as when we receive the iron from the factory?
 
4. Or perhaps the activity starts when we merely think about getting organized for its execution?
 
As seen in the example, defining the start of a task (activity) is not straightforward, and each person’s answer to whether the activity has started can vary significantly based on their interests:
  • If the goal is to get paid, the answer might be: Definitely! We’ve started!
  • If the goal is to demonstrate efficiency and minimize task duration (and maybe earn extra for the acceleration), the answer might be: Wait… we haven’t started yet!
Therefore, milestones that describe the start of tasks (activities) are extremely rare.
 
There is one exceptional milestone that proves the rule: NTP (Note To Proceed).
It initiates all project work – it defines the start of work. It’s essential to note that it effectively concludes the work of the project entrepreneur: signing contracts, handshakes, and the “passing of the baton” to the one that executes the project.
 
Milestones in a project should represent the completion of activities (tasks) and be linked using FS links with their preceding activities (tasks).

When, after all, do we encounter situations where a milestone is connected to the preceding activity with an SS link?

1. Suppose we have Activity C that precedes Activity A, and Activity A precedes Activity B in an SS Link, as shown here:

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

During an update, we realize that Activity B is canceled. Therefore, we reset the duration of Activity B, creating a situation akin to a “pseudo milestone”: (Why not use the “inactive” button? The answer is here.)

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

In the HCP-Go report, we will receive a comment regarding activities A and B – that they need to be corrected.

To correct it, we disconnect B from A (which was incorrect anyway) and link C (as predecessor) to B (the successor):

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

2. Another possibility we may encounter in this situation is the definition of project planners.
As we’ve seen earlier, this definition isn’t ideal because defining the start of an activity is quite challenging. Even in this case, my recommendation is to disconnect B from A and link B as successor to C.

Special Cases (ii): The Predecessor is a Milestone with a 'Finish-to-Finish' (FF) Link.

The scenario looks like this in the schedule Gantt chart:

Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

In this case, we have Task/Activity II, which we want to complete execution by the milestone’s end date. Therefore, the activity must start before the milestone, so it needs to precede the milestone. The result in the schedule: a milestone that precedes (i.e., comes before the activity) in an FF link.

Logical, right? 🤔 Not at all.

When do we encounter situations where a milestone is linked to a successor?

When does this happen? It occurs when we think about the project from the end to the beginning and construct links accordingly.

When we say, “I need to complete this activity by the milestone,” we link the milestone as a predecessor to the activity in an FF link.

However, a word of caution: While mental flexibility is excellent, in reality, we can only execute the project from today onward.
The activity must occur before the milestone, so it needs to precede the milestone.

It’s impossible to go back in time by 10 days because we need to complete the milestone in 5 days, and the activity requires 15 working days. Therefore, it’s a mistake to construct the Gantt chart this way.

In other words, if such a situation occurs in a project, there are two possible solutions:

  1. The activity needs to finish before the milestone. In other words, we should change the link: the activity should precede the milestone in an FS Link. We need to ensure that the activity has true predecessors based on the execution sequence.
Linking Milestones with SS (Start-to-Start) or FF (Finish-to-Finish) Links in Schedules

2. If there is no logical connection between the milestone and the task, but we simply want the activity to finish by a specific date and decide to link it to the milestone in an FF Link, then in this situation, it’s better to link the activity to a preceding activity that genuinely triggers its start and disconnect it from the milestone.

With HCP-Go, project managers complete
the project successfully.
Want to talk to Tal Levanon about it?

If you answered 'yes' - then we have a solution for you!

Leave a Reply

Skip to content