When implementing the Kanban method, how do you know how much work has actually been done and how much is in progress? Perhaps more importantly, how can you assess your workflow efficiency? The cumulative flow diagram (or CFD) is a crucial Kanban analytics tool, and provides an overview of the current state of your project. It can be used to help you identify issues that may be affecting your team performance.

When your process is about to face setbacks, you’ll see it first in the cumulative flow diagram. Read on to learn how to use the CFD to calculate average throughput, approximate average cycle times and gain insights into process bottlenecks.

What is a Kanban cumulative flow diagram?

The cumulative flow diagram tracks the total number of work items in progress each day. It is called “cumulative” because the values are accumulated over time.

Cumulative Flow Diagram

The cumulative flow diagram shows tasks distribution along the process stages. The graph is built from coloured bands of tasks, with each band indicating how many tasks are present in each stage of the process at a given time.

The vertical axis shows the number of tasks, while time is plotted on the horizontal axis. The curves are essentially the number of items in any process state, shown over time.

From the key, we have 3 groups of tasks:

  • To Do
  • In Progress
  • Done

These terms are the basic process steps which are the core of any Kanban board. Whenever your team pulls a new task and starts working on it, it is applied to the CFD by incrementing the “In Progress” curve by one. Logically, the “Done” curve is only increased once the task has been completed and delivered.

The Kanban cumulative flow diagram is built up slowly – by tracking and accumulating every task which enters your project workflow, the diagram shows the clear flow of all tasks through your process. When a problem occurs, rather than staying smooth and gently rising, the graph will show a sudden jump upwards. The transition can be spotted instantly, making the CFD a powerful tool for every Kanban team.

Reading the cumulative flow diagram

There is a lot of critical flow information which can be drawn from the CFD at a glance. You can analyse your process in more depth by learning to recognise the most common CFD patterns. By tracking the duration of each task, teams can see how quickly they are delivering work.

The gradient of the CFD curves are used to observe changes in work in progress amounts. A sharp increase in slope gradient would occur if your team is doing too many things at once. Such type of impediments visually show how stable your process is.

Work in Progress

One cornerstone of the Kanban method is that teams limit Work in Progress (WIP) to improve the quality and speed of delivery. The larger your WIP, the more tasks your team is attempting to complete simultaneously. This usually leads to constant context switching – a major source of low productivity and progress stagnation.

If the “work-in-progress” area is constant or decreasing with time, this is usually a positive sign for your team: you are meeting demand and delivering your product at a consistent pace. If WIP is growing, this may suggest a bottleneck or some other problem stemming the workflow.

When examining any Kanban CFD, the first area to check up on is always work in progress. Remember to account for any changes in work conditions (team size, change of personnel) before leaping to conclusions – these could provide explanations for unexpected spikes in activity.

Average throughput

When looking at a CFD, you can check how much is actually being achieved. In other words, you can evaluate how steep the “Done” area is. If the team is very productive and well-suited to the job, they will be able to complete tasks quickly: the “Done” pile will quickly grow.

You can easily calculate your exact average throughput for a certain time range. If the bottom line of your CFD represents the “Done” state from your process, then the slope of that line between any two points is your average throughput between those two points.

Approximate average cycle times

On the other hand, if we fail to do a good job, then the “Done” area would be flatter. If we are slow to deliver, then it means that our cycle times are larger. Reducing the cycle time, without sacrificing the quality of output, is a constant goal for Kanban teams. The faster a product is delivered, the more satisfied the client is.

You can measure approximate average cycle time by calculating the horizontal difference between the top line and bottom line of a CFD at any point along the graph. The cycle time is a strong indicator of the efficiency of work processes, since it reflects how quickly a project is completed after work has begun. This is directly related to the work in progress, and shortening cycle times usually means increased customer satisfaction.

 

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Enhancing the Kanban method

The Kanban method is built around optimising cycle times, limiting Work in Progress, and continuously delivering – implementing incremental, evolutionary change. By showing the accumulation of tasks completed over time, the cumulative flow diagram provides compelling visual evidence to show where these changes need to be made.

The fundamental purpose of the Kanban cumulative flow diagram is to demonstrate the stability of your workflow. Analysis of the CFD should tell you what areas need your focus, in order to maintain continuous process improvement. It enables you to improve your overall productivity and efficiency.

If you have used cumulative flow diagrams within your team, we’d love to hear what effect they had on your performance. Share your story in the comments below!

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