To estimate (or not) in Kanban? Leveraging lean thinking to eliminate waste

Let’s start with listing synonyms of the word estimate: calculate roughly, approximate, guess; and a common definition of the word estimate: “to judge tentatively or approximately the value, worth, or significance of“. My favorite way to illustrate an estimate is simple: not accurate. There is nothing wrong with that unless the people requesting or using this estimate don’t understand what the word actually means…

How often have you received this request from your manager: “Can you work more on this estimate, please make it more accurate“. This is the fundamental problem with having estimates, they are not meant to be accurate, and that’s ok because they are estimates! So should we use estimates? It depends on why, when, and what you need the estimate in the first place.

When we think of Kanban, how do we estimate the work on a Kanban board?

The best way to illustrate this concept is to consider how amusement parks know the wait time when you are waiting in line for a ride…

The technique is simple, if the attraction can load 20 people per ride and each ride takes 3 minutes, then a sign can be posted roughly where the 200th person waiting line would stand to inform them of a 30-minute wait time. It requires a little bit of math (3 minutes x 10 = 30 minutes and 20 people x 10  = 200 people), but it’s a very simple and effective way to set the right expectation for the users of this system. This data point is not accurate, but good enough for the user to make a decision about the value of the attraction vs. waiting in line for 30 minutes.

Let’s apply this to a Kanban board. After using the board for a few weeks, the team has figured out that the average time a card (or work item) takes to flow on the board is 3 minutes, and the Work in Progress (WIP) limit on this board is 20 cards. Using the same numbers and math applied in the attraction ride example above, a card positioned roughly as the 200th card in the “To Do” column of the Kanban board would get completed in roughly 30 minutes.

Both the attraction ride and the Kanban board might have changes in their line or backlog of work. In the attraction ride example, some people might leave the line, or others might cut in front of people in this line, but minor modifications like this should not impact the estimate because it’s only an estimate. On the Kanban board, we can imagine that people might change their minds about the work contained in a card or add new work in front of the card you are trying to estimate. If the changes are minor, then the estimate should still be inaccurate but close enough. On the other hand, if 100 new cards have displaced the original card from the 200th spot in the backlog to the 300th spot, then the new estimate should be roughly 45 minutes.

So should we estimate each card (or work item) in Kanban?

Or should we use simple math to provide the same result? In my experience with Lean Thinking, the first principle is to identify and eliminate waste. Is the act of creating estimates wasteful? On a Kanban team where the work is produced by experts of the work flowing through the Kanban board, and this work is complicated but not complex (i.e.: the experts know how to do the work), then why spend any time creating estimates that will be wrong at the single card level? This is the beauty of Kanban, the experts learn over time to break all their work into cards that are roughly the same size; therefore just like people waiting in line, the cards on a Kanban board follow the same principle.

The decision is yours. Would you prefer your experts to deliver valuable work or to continuously interrupt them to provide inaccurate estimates? Remember that the most damaging action on productivity is to cause your experts to task switch. Unless estimation is part of your Kanban process as an explicit exit criterion for one of your Kanban board columns, I would greatly advise you to not disrupt the flow of your work.  Asking an expert to stop working on their current task to think of something that is not tangible yet and far in the future is an absolute waste of productivity.

As you ponder this idea of no longer creating estimates on your Kanban cards, please take into consideration that Kanban provides a few critical metrics to help you gather all these data points. Learn more about Cycle Time and Throughput reports so that you can make wise decisions about estimating (or not) in Kanban.