Sometimes a task does not line up perfectly with its predecessor. Instead of setting the task to manual and removing its dependency, lag and lead time can be applied to the task to have it start earlier or later. In MS Project adding lag or lead time is a simple process of editing the dependency and either adding or removing time.
First, we need to understand the different types of dependencies and their codes in MS Project. There are four dependency types:
Finish to Start (FS) – Task cannot start until predecessor finishes (Default)
Start to Start (SS) – Task cannot start until predecessor starts
Finish to Finish (FF) – Task cannot finish until predecessor finishes
Start to Finish (SF) Task 8 cannot finish until Task 7 starts
A normal dependency would be coded in either the Predecessor or Successor column as such: [Task Number][Dependency Type] (Ex: “24FS”, “15FF”). If you do not specify the dependency type the system defaults to Finish to Start (FS). Lead or Lag time is entered after the dependency type. If the task needs to be delayed with lag you would enter a “+” sign followed by a number and then either “d” or “w” to specific days or weeks. Lead time is subtracted from the task so you would use a “-“ instead.
Let’s say Task 2 needs to start 5 days before Task 1 Finishes. In the predecessor column of task 2 you would enter “1FS-5d”. If you would like to add lag instead of subtracting lead time it would look like this: “1FS+5d”.
It is always best practice to use automatic tasks versus manually scheduled tasks. Some users struggle with using the scheduling engine, but by using lag and lead time you can easily control your tasks while still staying in automatic task mode.
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