Easy task estimation with Three-point estimation technique

You may also like...

  • Abid Ali

    but how will we know that worst case is 10 days while concrete need 14 to 28 days to get its full strength

  • Anonymous

    Shouldn’t that be:

    SD = 7/6
    SD = 1.167
    SD = 1.67

  • how do you calculate confidence level or percentage

  • Great article Zoran!

    The Standard Deviation looks like an “estimated standard deviation”.
    Do you use this estimation due the few data items to analyze?

    How long have you applied these techniques on production environment?


    • Hi Gustavo,
      Thanks for commenting!

      Actually I heard about this technique in one of the “Project Management” courses I’ve attended last year and then thought that it would be nice to post it. And no, I am not a project manager; at least not “branded” as a such:)

      I find this quite useful whenever there are tasks that are really hard to estimate, indeed we call this kind of estimations -> guesstimations. Often I get asked about “how long does it take” without clear requirements, and without any clue what need to be changed, so this kind of range is guessed.

      In reality, you won’t really need to do this if you have well defined tasks and by definition tasks should be not more than 5 days work otherwise those need to be split up. As soon as you start analyzing big stories into smaller tasks, this technique is really not needed.


  • Duncan Creasey

    wondered how you got the standard deviation to be 1.67 as in excel it calculated as 0.89
    I can understand the E value given beforehand as a weighted average but not the SD calculation.


    • Hi Duncan,
      Thank you for your comment. What kind of calculation have you done in Excel?
      The given Standard Deviation calculation is expressed in the so called L-estimator.
      Please check for more info on wikipedia by following this link: https://en.wikipedia.org/wiki/L-estimator


    • @Duncan
      I thik that this is an “estimated” standard deviation due the few items to analyse.

      How long do you apply these techniques on production software?


    • Ben

      In Excel the standard deviation formula is for a given population. Triangular and the given beta distribution are estimates based on statistics and they are not calculated the same way. The beta distribution provided is one possibility coming from PERT. I don’t know much more than that. In Excel the formula to use will be beta-something, but I don’t know what parameter (part of the assumption made in PERT) to use to get this specific PERT-beta distribution. Just use it as it is 😉