Project management

5 tips to get the most accurate estimates possible

Psoda blog author avatar
20 March 2018

One of the hardest parts of building a project schedule for me is getting accurate estimates for tasks. It’s made more difficult when people outside of the project see the GANTT chart and think the estimates have come out of an objective process, rather than one person’s subjective gut feel.
For example, how often have you heard, or taken part in, a conversation like this:
“Hi Joe, how long will it take you to build the database?”
“Do you mean the complete version or just a rough working model?”
“The final thing”
“I think about six months all up.”
“You think? I need something a bit more concrete.”
“OK, six months all going well, but this isn’t accurate so don’t quote me.”
“Perfect, six months it is!”
The project schedule then shows the database build will take six months to complete.
I’m as guilty of doing this as anyone and it’s come back to bite me on more than one occasion. So how do you go about getting the most accurate estimates possible? Here’s some tips I’ve learnt over the years:

  1. Always give people time to come up with the estimates. I’ve found that the estimates I receive when I’ve rushed people, tend to be overoptimistic and often need to be changed at regular intervals
  2. Try to give the estimator as much information as possible up front. It’s impossible to give an accurate estimate without having all of the information available
  3. Make sure you ask the right people to give you the estimates. There’s no point asking someone who has never done a particular job before to tell you how long it will take. That might be stating the obvious, but I’ve seen it happen on more than one occasion, with the predictable results
  4. Get the estimators to provide three figures for each task – the best estimate, the most likely estimate and the worst-case estimate
  5. Try and use bottom up estimating where possible. It is the most time consuming, but tends to give the most accurate results

I hope these tips help the next time you need to do some estimating on your project.
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Rhona Aylward avatar
Written by Rhona Aylward
Rhona is Deputy Everything Officer at Psoda, where she does everything except code. After starting life as a microbiologist she moved into PMO leadership roles around the world before settling in New Zealand with her family.

1 Comment

  • FantasiasMadrid says:

    If this had been laid out clearly up front in either of the two math stats books I read (DeGroot and Schervish, Larsen and Marx), it would”ve made my life a lot easier. They tend not to get to estimators until the end of these books after hacking through a ton of seemingly random (pun intended) hypothesis tests.

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