Home > Agile, Leadership, planning > Why don’t your estimates improve?

Why don’t your estimates improve?

One question I often get is why the estimates given by developers are so bad. Why they don’t become better.

If you look at what people have estimated for the longest time, one guess is weather. I can imagine early humanoids taking a glance at the sky in the morning, estimating if this is a good day for hunting or what ever. So, our weather for casts should be great?

Well, that depends.

Having just visited Greece this summer, I became after just a couple of days an expert on weather predictions for Rhodes. It’s hot, warm and windy and when I look at the for cast for the upcoming week, I think my guess is as good as the pro’s:


But I live in Sweden and if I’m going to make an estimate of the weather for cast for the coming week, my guess is probably bad. The weather fluctuate more in our temperate climate.


So, when you think that your developers never “learn how to make accurate estimates”, think about the surroundings. Is the system in a temperate climate or is the weather steady as in Rhodes?

Another important lesson is that estimates are given at a specific moment. If I’m going to guess the weather in Stockholm August 13th 2010, my guess will be a pure guess, since I have no idea of the weather situation then. I can make a better guess about August 13th 2009, since that date is pretty close. So, even if you can make a prediction, this will change over time. This mean that an estimate concerning size of a task is valid just then. A month later, when the systems have changed a bit, that item can have become more or less expensive. So, don’t get upset with that developer because he gave you an estimate a year ago and he won’t hear about that today. If you want to place yourself in his position, consider the task of “getting ready in the morning”. Imagine yourself being asked that question when you are a 27-year-old without kids. Do you think that your estimate of getting ready in the morning in that situation is valid three years later when that 29-year-old has a child which goes to daycare. Just like our situation becomes more and less complicated, so becomes the situation for systems.

So, for how long is an estimate valid? Well, that is something which differs between systems and organizations. So, this you need to find out for yourself.

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  1. 2009/08/12 at 5:24 pm

    Good post! I believe that estimates degrade within 5 iterations or 4 months (my raw guess). I think all untouched stories or items on the backlog should be revisited every now and then to see if they are still valuable and estimated correctly. This results in low priority stories getting “graveyarded” and estimates getting realigned.

    As for humans being good/bad at estimating, Linda Rising presented an amazing lecture on this topic at Agile 2007. I can’t distribute the slides openly, but if you want a copy… email me directly.

  2. 2009/08/31 at 9:30 am

    I personally believe that another dimension of uncertainty in estimation is whether you develop a new software or whether you simply extend an existing one. As soon as we are forced to work in a new environment with components or software that we do not fully know, we become uncertain and or estimates will in some sense reflect ths uncertainty.

    • Anna Forss
      2009/08/31 at 3:12 pm

      @andreas. that is very true. there are many such aspects. also if it’s a tested or untested software. when you estimate, you estimate cost and benefit but you should also estimate risk from both business and technical aspect.

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