Task Estimate Confidence

What level of confidence do you have in your Task Estimates? Who estimates the tasks and what methodology do they use?

I have found that despite all efforts to construct a schedule that delivers the project on time, if the task estimates are wrong — the schedule will fail.

I have built many schedules that required re-baselining. This caused me to study why these initial schedules were so poor. What I found primarily was that the task definitions were poor, and secondarily that the task estimations were poor. As a result of these findings, I added 2 techniques to my methods:

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1) The task must have a proper definition — confirmed by the resource. You can read about these methods here:

2)   The Resource who works the task is the one who estimates the task using a pre-defined method for estimating.


It is very important to coach and build proper rapport with your resource. They need to know that you care about their success. You can do this by asking a few simple questions and listening carefully to their response:

  • Have you reviewed the task definition, and do you fully understand it?
  • Have you worked this task before?
  • What confidence do you have in your estimate of the time required to complete the task?

So, let’s take a look at how resource confidence and the task estimates are related. Here is a typical distribution of the time needed to complete a task:

The distribution plots how frequently a specific time to completion occurs. The area under the curve is the total probability of task completion. 

Reading the distribution from left to right notice that:

  • No tasks are completed in zero time
  • As the time to complete the increases, the number of occurrences increases up to a point of maximum occurrence
  • After the maximum occurrence, the occurrence decreases as the time to complete increases

Now consider your resource. What odds of success do you want them to have — 50/50? Not likely, and I hope not. You need your resource to be confident in completing their task on or ahead of schedule.

There is a balance to be found between high confidence and an overly inflated task estimate. I have found the sweet spot to be about 85% and encourage my resources to provide an estimate where their confidence is at least 80%.

The statistics show that at an 80% confidence, the time to complete the task is approximately 3 times greater than the time to complete it at a 50% confidence.  In other words, asking the resource to estimate the task at an 80% confidence will produce an estimate that is 200% larger than at a 50% confidence.  I define this as the task Safety.

Some schedulers remove the safety and build their schedule using the 50% confidence estimate. They might store the safety as contingency elsewhere in the schedule, but this drives the resource to work at 50% confidence level knowing that failure occurs half of the time. Personally, I believe managing this way is disrespectful and a demotivating force on the resource.

What has worked well for me is to trust the resource, give them the confidence for success, and support them in every way possible to achieve it.


steven souther

Steven Souther is the creator of the Lagility Method. When he's not developing outstanding task methods & tools, he explores the underwater world of the seas. Learn more

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