The document discusses two methods for calculating early start (ES) and late finish (LF) dates in a network diagram. The first method assumes the start activity has ES, EF, LS and LF as 1, while the second method assumes these values are 0. The document advises that either approach can be used, but in practice most scheduling tools use the second approach of starting from day 1 rather than day 0. It notes exam questions will make clear which approach to use for calculations.

1. PMP® Exam Tip: Calculating ES/FS
We recently received the following question from
a Project Management Professional (PMP)® Exam
Student:
“There's some confusion in my head with regards to
some of the network diagram calculations. I'm lead
to believe there are actually two methods to
calculate ES, LF, ES etc etc.
The first method adds or subtracts 1 where
applicable. This assumes that the start activity has
ES, EF, LS and LF as 1. The second method assumes
the start activity has zeros for all values thereby not
having to add or subtract 1 to any of the formulas.
Is there any indication in the exam that would lead
me into knowing which "method" is being utilized so
that I can apply the right formula?”
I answered that he is correct. there are indeed 2
approaches:
- First approach: You calculate the network diagram starting on day 0
- Second approach: You calculate the network diagram starting on day 1
I personally use the second approach, because when my sponsor tells me that my project starts
on the first day of September, then that is September 1 and not September 0. This is also the
way that all modern scheduling tools seem to work. You schedule your project based on a
calendar start date and not "on day 0".
That is why there is a slight difference between the calculations (you have to add/subtract 1
from the results in the 2nd approach). However, don't worry about this for the exam too much.
The way that the question is formulated, you should be able to identify how to go about this.
Also: I understand that in most cases when you have to calculate this, it is the end result that is
important and not how you got there.
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