How to calculate float, free float and total float using ES is part of the project management.

The difference between activity ES and LS is mentioned on the page.Links to other differences between terms are also provided.

Early Start is when activity can start.If all the previous activities in the path started early, an activity near the end of path will start.This activity will be pushed out if any of the previous activities slip up.

The earliest time that an activity can finish is called Early Finish.If all previous activities started early and no activities slipped, it is the date that an acitivity can finish.

The project manager and team will know how much freedom they have to move the start and finish dates without causing any problems to the project.

Late Start is when an activity can start.It is possible for an activity to start late if it is on a path that is shorter than the critical path.If other activities slip, these delays will cause a problem.

The latest time that an activity can finish is called Late Finish.If an activity is on a shorter path and all of the other activities are on the same path, then it can finish early and not cause the project to be late.

Knowing late start and late finish will allow you to see how much can be played.There are more options if an activity has large LS andLF.

If two activities converge, the first activity will be 1 ES of all other activites.The direction from left to right as you traverse on the network diagram is shown in fig-1.The example-1 depicts early start and early finish calculations.

For all other activities except the convergence mentioned in the next line, theLF is the same as the last activity.The reverse pass is the direction from right to left as you traverse on the network diagram.The example-2 depicts the Early Start and Early Finish calculations.