Estimating most projects is necessarily an imprecise exercise. The goal of this post is to share some tools I’ve learned to remove those sources of error. Not all of those tools will apply to every project, though, so use this more as a reminder of things to consider when estimating, rather than a strict checklist of things you must do for every project. As always, you are the expert doing the estimating, so it is up to your own best judgement.

Break things into small pieces

When estimating, error is generally reduced by dividing tasks into more and smaller pieces of work. As the tasks get smaller, several beneficial things result:

• Smaller tasks are generally better understood, and it is easier to compare the task to one of known duration (e.g., some prior piece of work).
• The error on a smaller task is generally smaller than the error on a small task. That is, if you’re off by 50% on an 8 hour task, you’re off by 4 hours. If you’re off by 50% on an 8 day task, you’re off by 4 days.
• You’re more likely to forget to account for some part of work in a longer task than a shorter one.

As a general rule, it’s a good idea to break a project down into tasks of less than 2 days duration, but your project may be different. Pick a standard which makes sense for the size of project and level of accuracy you need.

Count what can be counted

When estimating a large project, it is often the case that it is made up of many similar parts. Perhaps it’s an activity which is repeated a number of times, or perhaps there’s some symmetry to the overall structure of the thing being created. Whichever way, try to figure out if there’s something you already know which is countable, and then try to work out how much time each one requires. You may even be able to time yourself doing one of those repeated items so your estimate is that much more accurate.

Establish a range

When estimating individual tasks (i.e., those which can’t be further subdivided), it is often beneficial to start out by figuring out the range of possible durations. Start by asking yourself: “If everything went perfectly, what is the shortest time I could imagine this taking?” Then, turn it around: “If everything went completely pear-shaped, what shortest duration I’d be willing to bet my life on?” This gives you a best/worse-case scenario. Now, with all the ways it could go wrong in mind, make a guess about how long you really think it will take.

Get a second opinion

It’s often helpful to get multiple people to estimate the same project, but you can lose a lot of the value in doing so if the different people influence each other prematurely. To avoid that, consider using planning poker. With this technique, each estimator comes up with their own estimate without revealing it to the others. Then, once everyone is finished, they all compare estimates.

Naturally, there are going to be some differences from one person to the next. When these are small, taking an average of all the estimates is fine. However, when the differences are large, it’s often a sign that there’s some disagreement about the scope of the project, what work is required to complete it, or the risks involved in doing so. At this point, it’s good for everyone to talk about how they arrived at their own estimates, and then do another round of private estimates. The tendency is for the numbers to converge pretty rapidly with only a few rounds.

Perform a reality check

Oftentimes, one is asked to estimate a project which is at least similar to a project one has already completed. However, when coming up with a quick estimate, it’s easy to just trust to one’s intuition about how long things will take rather than really examining specific knowledge of particular past projects to see what you can learn. Here’s a set of questions you can ask yourself to try to dredge up that knowledge:

• The last time you did this, how long was it from when you started to when you actually moved on to another project?
• What is the riskiest part of this project? What is the worst-case scenario for how long that might take?
• The last time you did this, what parts took longer than expected?
• The last time you did this, what did you forget to include in your estimate?
• How many times have you done this before? How much “learning time” will you need this time around?
• Do already you have all the tools you need to start? Do you already know how to use them all?

There are loads of other questions you might ask yourself along these lines, and the really good ones will be those which force you to remember why that similar project you’re thinking of was harder / took longer / was more expensive than you expected it to be.

Create an estimation checklist

If you are planning to do a lot of estimating, it can be immensely helpful to cultivate an estimation checklist. This is a list of all the “parts” of the projects you’ve done before. Naturally, this will vary considerably from one kind of project to the next, and not every item in the checklist will apply to every new project, but they can be immensely valuable in helping you not forget things. In my personal experience, I’ve seen more projects be late from the things which were never in the plan, than from things which took longer than expected.

✧✧✧

Estimation is super hard, and there’s really no getting around that. You’re always going to have some error bars around your estimates, and, depending upon the part of the project you’re estimating, perhaps some considerably large ones. Fortunately, a lot of people have been thinking about this for a long while, and there are a lot tricks you can use, and a lot of books on the subject you can read, if you’d like to get better. Here’s one I found particularly useful which describes a lot of what I’ve just talked about, and more: