A service level expectation is a probabilistic forecast of how long it will take a single item to pass through the system. For example: “85% chance of completing in four days or less”.
The SLE is part of the definition of workflow and is one of the mandatory pieces of your kanban system.
How do we determine the SLE?
When the system is first being set up, we may have to make an educated guess about what the SLE will be. The moment work starts to flow through the system, however, this becomes something that we measure, not guess. Looking at this cycletime scatterplot below, we can see that 85% of all the historical work in this time period completed in nine days or less. That’s our SLE.
So now if someone asks us when a new request will be done, we know that if we started it right away, we’d have an 85% chance of completing in 9 days or less.
What’s the difference between a Service Level Expectation (SLE) and a Service Level Agreement (SLA)? An SLA typically comes with a penalty. If you miss the SLA there may be monetary penalties for that. The SLE on the other hand, is a forecast, not a promise.