Time Management Questions

1)An activity has an early start (ES) of day 3 , LS of day 13 ,EF of 9 and LFof 19 . What is the duration of the activity







Please provide the answer with explantion


You have project with four activities . Activity 1 can start immediately and has an estimated duration of one . Activity 2 can start after activity 1 is completed and has an estimated duration of four.Activity 3 can start after activity 2 is completed and has an estimated duration of 5 . Activity 4 can start after activity 1 is completed and must be completed when activity 3 is completed.The estimate for activity 4 is 10 . What is the shortest amount of time in which the project can be completed






Answer = 3) 11


Consider that Activity 3 and Activity 4 both finish at the same time.

Duration of project = dur Act 1 + dur Act 4 = 1 + 10 = 11





ES = Day 3, EF = Day 9

Activity gets performed on days 3, 4, 5, 6, 7, 8, 9 => Duration = 7 days


Alternatively, LS = Day 13, LF = Day 19

Activity gets performed on days 13, 14, 15, 16, 17, 18, 19 =>  Duration = 7 days



Thank you..

 ef-es =9-3= 6 

I have come across many blogs / posts wherein it was said that PMI always follows the zero start method. So when nothing is given in the question by which you can determine the method, we should always go by zero start method which is the PMI way.

Now, in the 1st question, as per zero start method, you should subtract early start from early finish to get the duration.

Duration = EF - ES = 9-3 = 6

I agree with AP, it has to be 9-3 = 6 Days

Even if we consider both schools of thought - 'Start from 0'  and  'Start from 1' - the calculations here involve subtraction and hence the offset would be compensated for.

** Pls note that some formulae could be different for each method for the end results to be consistent. **

I am noticing that this 0 vs 1 topic has a history to it... lots of blogging and controversy!

Andy Crowe and O'Reilly appear to use 1 as the Start time. Rita uses 0. PMBOK 5th ed seems to use 1 as the Start time.

I looked at Rita 6th ed and it says that there is no right way. Pick a method and use it consistently and you will get the correct answer. PAGE 198.

Even if PMI (PMBOK 4th ed) uses 0 as the start time, the final result should match that obtained from using 1 as the start time.


Q #1: Can you please point me to a reference for the formula used by you above: Duration = EF - ES ?

 Q #2: If you map the activity days to a calendar week, or finger-count the no of days, would you still get  a duration of 6?

Day 0 = Sunday, Day 1 = Monday, ..................., Day 6 = Saturday.



Q #1: Please don't treat this as a formula. This is drevied from logic.

Q #2: When you use zero start method, even if the ES is written as 0, logically the count should start from 1 when you use fingers to count. Hence the duration will still be 6.

I saw all of you guys using  'EF - ES = Duration'  above, hence I asked for a reference, but sure we can look at it logically.


** Are the EF Day and the ES Day (and even Day 0, for that matter) considered FULL days of work or not? Does the source of discrepancy lie here?

** We can count in this way:

Day 3 (ES day) => count = 1

Day 4 => count = 2

Day 5 => count = 3

Day 6 => count = 4

Day 7 => count = 5

Day 8 => count = 6

Day 9 (EF day) => count = 7



Your analysis is perfect and correct but it represents 1 start method and not zero start. According to zero start,

Day 3 (ES day) => count = 0

Day 4 => count = 1

Day 5 => count = 2

Day 6 => count = 3

Day 7 => count = 4

Day 8 => count = 5

Day 9 (EF day) => count = 6

PMI suggests to use zero start. Duration will vary by a day between these two methods. If there are more details in the question, you can determine which method they have used and you can answer accordingly. But when the method cannot be determined from the given data, it is always better to go by PMI way.

I may be wrong, but this is how I understood the concepts when I was preparing for my exam by going through various blogs and forum.

I don't mean to drag this on forever. Pls bear with me just for a moment. You had earlier replied:

"Q #2: When you use zero start method, even if the ES is written as 0, logically the count should start from 1 when you use fingers to count. Hence the duration will still be 6."

However, in your most recent post you have started counting from 0. But for finger counting we need to start from 1.

My initial observations with the very limited reading that I have done:

1.  With the 0 method, the very meaning (English language, common sense meaning) of the word 'duration' is getting distorted. E.g. I know that a task takes 56 hours of effort. With an 8 hr workday, it makes for a 7 day duration. But now if I start scheduling with 0 Start method, I suddenly start saying that the duration of this task is 6 days. That seems weird.

2.  I would suggest that the Duration in 0 Start method is not the real duration of effort... it is merely a temporary work-in-progress variable to be used. That makes it feel so much better :)

3.  I could not yet find any official PMI reference for using Start from Day 0 method. If someone can please point me, I will appreciate.

4.  The fact that PMBOK 5th ed refers to Start from 1, indicates that PMI likes to Start from 1. REF: Figure 6-18, pg 177.

5.  The ES, EF, LS, LF values are different in both methods.

6.  I have not yet seen any text where Duration calculation from ES, EF, LS, LF is explained using 0 Start. But Andy Crowe has explained it using Start from 1.

7.  Start 0 method seems to be a product of s/w programming where arrays can start from 0th position. Element no 6 in an array is actually the 7th value, since the array starts at position 0.

To clarify, I don't have a problem with either method, but I would say that the results should be consistent. Hopefully if I get some free time, I will compare the results from both methods and post a brief summary.

Sorry for the long winded post...


After a long drive with this stuff on my mind, I now think...

1.  Durations are normally provided in the CPM/network question itself as raw data, so both 0-Start and 1-Start methods will use the same provided duration values. GOOD.

2.  The Critical Path duration and the path itself *must* come out to be the same using either method. GOOD, IF TRUE. I have not tried this.

3.  Various float values should be identical across both methods. GOOD.

4. The ES, EF, LS, LF values will be different for both methods. BAD side effect.

5.  **** Computing duration from ES, EF, LS, LF values seems like a bad idea... and should not be asked to be done.

6.  0-Start method appears to be - sorry to say - contrary to basic logical thinking. It might give correct answers but that does not mean that it fits with with our natural way of thinking. It's like saying "My age is 7, but hey I'm 6 yrs old... because I count from 0."

7.  I suspect most of the controversy is merely amongst all of us - PMP aspirants and tutors... I am sure the actual PMP exam questions are unambiguous and solid.

Bottom line: Pick a method, use it consistently and hope that the exam has solid and clear questions (which I am sure it does).


 whats the answer for Q1 ? Is it not 6 ..Guys please confirm..Let us not stay with wrong answer

In place of - let us not stay with wrong answer.

I would like to say - let us not stay with wrong question.

 Hi pmp newster

i went through all your analysis and comments , all makes sense. I just want to give another perspective of thinking and this not referencing any books and totally on date calculations. Suppose someone give me one day of march to do some work..so it means that I have 3/1/13. Again I got another day work..and now I have 3/2/2013. So now if some asks me how many days I work I am going to subtract my two dates... 3/2 - 3/1 and it give me one day..that's not true actually I worked for two days!! And if I says in march I worked upto 3/2 and at that time straightforward ppl will say oh so you worked for two days actually they are subtracting from zero ( note date starts from 1 not zero) or doing 3/2-3/1 plus one day,to come with 2 days. Pm plan will show

task1 - 3/1/13(start) and end date(3/1/13) duration 0 to 1 day

task2 -3/2/13(start) and end date(3/2/13) duration 1 day.

now that zero process task1 you will say es=0 and ef=1 => duration 1-0=1 day

1day method for task 1... es=1 and ef=1,so duration is 1-1 plus 1 day. So duration is 1day for task 1.

so to me one day method makes sense as it does calculation based on dates, so I will follow 1day method as it much aligned with date calculation that project managers follows( here I means project plans we develops),So my answer is 9 - 3 + 1 and second you.

I agree this type of questions drag everyone analysis ..so we should be okay that we all are thinking :) and have disagreement lol

 See below errata: first time PMI published errata on PMBOK (it is errata of PMBOK -5)



177           Figure 6-18--Added the following clarifying the note to the figure. This example uses the accepted convention of the project starting on day 1 for calculating calendar start and finish dates. There are other accepted conventions that may be used