EARLY START (ES)
The earliest date a task can start.
EARLY FINISH (EF)
The earliest date a task can be completed
LATE START (LS)
The latest date a task can start without delaying the project end date
LATE FINISH (LF)
The latest date a task can finish without delaying the project end date
Calculate the Earliest Time
The calculation process begins with placing a zero in the Early Start (ES) position of the first activity. The rest of the calculation continues with the use of the following formulas:
Early Start = ES value from immediate Predecessor(s) + Duration.
Calculate the Latest Time
Calculate the latest times each task can start and finish without upsetting the project schedule, based on how long later tasks will take.
These are called the latest start (LS) and latest finish (LF).
Starting from the last task, where the latest finish is the project deadline, and working backward.
Latest start (LS): LF – Duration of the activity
How to calculate the earliest and latest time for Activity on Arrow