Are #Estimates Lies? #NoEstimates

One of the statements that causes me angst is the “Estimates are Lies” that I read on the Twitterverse from time to time. So I thought I’d do some research. I decided to look up the definition of a Lie.

lie is a false statement to a person or group made by another person or group who knows it is not the whole truth, intentionally. Lies can be told for various reasons and with various amounts of success.” – Wikipedia

Under this definition, an estimate is indeed a lie. We know the estimate will be incorrect. But doesn’t the whole statement depend on what the definition for truth is? 🙂

Truth is most often used to mean in accord with fact or reality” – Wikipedia

Hmmm, so it seems that under these definitions that estimates are indeed lies.


The only caveat to the above definitions is that estimates are a specific type of statement. They are a prediction. All predictions are lies by their very nature. We can never be exact about the future as things will always change. The further away the prediction, the greater chance our predictions or lies will be bigger.

So what is the definition of a prediction?

“A prediction (Latin præ-, “before,” and dicere, “to say”) or forecast is a statement about the way things will happen in the future, often but not always based on experience or knowledge. While there is much overlap between prediction and forecast, a prediction may be a statement that some outcome is expected, while a forecast is more specific, and may cover a range of possible outcomes.

Although guaranteed information about the future is in many cases impossible, prediction is necessary to allow plans to be made about possible developments; Howard H. Stevenson writes that prediction in business “… is at least two things: Important and hard” – Wikipedia


So it seems that estimates are both lies and predictions.

But this is a slippery slope. I tell my wife I will be home by 6 from a new location I have never driven home from before. Turns out I hit a traffic jam and I didn’t get home until 6:30. Did I lie to her? I would say no. I gave her the best answer I had at the time with the information I had and the experience I had. Sound familiar?  In my opinion, a prediction is only a lie if it isn’t my honest, and truthful best attempt at predicting the future.

Let’s state that again “In my opinion, a prediction is only a lie if it isn’t my honest, and truthful best attempt at predicting the future.”

Estimates will always be wrong, but estimates are not lies. They are a prediction given the best information we have at the time. And they are made to help the other person plan. If I refused to give an estimate of my arrival time and said I didn’t know and wouldn’t know until I got there, my wife could not have made plans to pick up the kids.  In our busy lifestyle, this is just not an option to wait until we both got home before we committed to any plans. This is a very simple example but it highlights the challenge of planning without any predictions.

To make plans that affect multiple people or groups or people, you need to make predictions. If you need to make predictions you need estimates. Whether estimates are lies or not is beside the point. We usually need them when working with different groups of people. Like businesses, families, or teams.

Final Caveat

I do agree that once you have direct experience that should replace prior estimates… Once I have traveled that route home a few times, I should use my experience to provide me with a better estimate. In Software Development projects, I should switch to using my velocity as soon as possible and not rely on the initial estimate anymore. Failure to do this corrupts the purpose of the estimate. It is only a prediction until we have more information.

Remember the definition of my estimate was “the best answer I had at the time with the information I had and the experience I had”. If I have new experience or knowledge I am obligated to use that information and re-estimate.

6 thoughts on “Are #Estimates Lies? #NoEstimates

  1. I think Merriam Webster has better definitions:
    intransitive verb
    1: to make an untrue statement with intent to deceive
    2: to create a false or misleading impression

    : a statement about what will happen or might happen in the future
    : the act of saying what will happen in the future : the act of predicting something

    Prediction seems to be applied to an estimate, but it isn’t a lie (as you say) 🙂

  2. Nice post. I think it goes well with my musings on “What does it mean for an estimate to be right?” (

  3. “The Clean Coder” by Robert C. Martin has a great, all be it concise, chapter on estimation. I don’t have the book with me right now so forgive me if I get this wrong but the gist of it is that most of the problems with estimates come from people’s differing definition of what an estimate actually is. To more business minded people it is seen as a commitment to a specific date or time period where developers see it as more of a “guess” of how long it should take us to compete a task. He views it more as a range, from optimistic to pessimistic with assigned probabilities of sub-ranges. He talks about the use of PERT and being brutally honest with both your optimistic and pessimistic numbers.

    I believe that if we could agree to a common definition of what an estimate actually is and use a more scientific approach to coming up with our estimates we could both make our estimates more meaningful and remove some of the animosity when estimates are off.

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