When using Primavera or when learning project management, you might have heard about late start, ate finish. I will explain here the early and late dates to help you easily understand what these dates are:
Let's say, the start date of my project is 1-January-2018.
The project has one activity (keeping the example simple). This activity can start on 1-January-2018. The earliest date this activity can possibly start is 1-January-2018. This is the activity's early start date. Now, let's say the duration of the activity is 20 days. So if this activity starts on 1-January-2018, the earliest it will finish is 20-January-2018. This is its early finish date.
Say the end date for my project is 30-December-2018.
My project has one activity only (again, keeping the example simple). The duration chosen for this activity is 10 days. Now, the latest date this activity will finish is 30-December-2018. This is the activity's late finish date. If this activity was to finish on 30 December, with 10 day duration, the latest date this activity will start is 20-December-2018. This is the activity's late start date.
This is the simple definition of early and late dates in project scheduling. I hope you found their definition easy to understand.
In project scheduling, the late dates are usually not used by anyone. Someone might just want to know what the late dates of the activities are in case they need to start an activity as late as possible in the project and finish it as late as possible.
In Primavera P6 software, there are columns - early start, early finish and late start, late finish. You can add them. Once you have scheduled your project (by pressing F9), these columns will show you early and late dates for all activities.