Applying the Backward Pass
The backward pass is used to calculate the LS and LF dates of all network activities. These are the latest dates these events can take place without affecting the finish date of the project.
For this example, assume that the LF of the activity following Pour Concrete is 15. To calculate the LS of Pour Concrete, take 15 and subtract 4, the duration of the activity, to get 11.
The LS of Pour Concrete is the LF for Mix Concrete. To calculate the LS for Mix Concrete, subtract the duration from the LF: 11 - 6 = 5. This means that Mix Concrete can start as late as day five without affecting the finish date of the project.
The LS calculation is LS = LF - duration.
Note that in the last activity of the project
the EF is the same as the LF. Using that
LF, you can start the backward pass.
Also note that the LS and LF numbers do
not equal the ES and EF on the bottom
path.