Cumulative flow diagrams allow you to succinctly visualize the entirety of your workflow and are useful tools in diagnosing problems within your processes. Using a cumulative flow diagram will help you reduce your average cycle time, manage your WIP limits, and increase your team’s throughput.
A cumulative flow diagram (CFD) is an advanced analytic tool in the Kanban method. It provides teams with a visualization of workflow efforts and overall project progress. The cumulative flow diagram allows teams to monitor how stable their workflow is, anticipate bottlenecks so they can adjust their workflow accordingly, and help make processes more predictable.
By graphing how tasks accumulate over time and their overall distribution across the process stages, cumulative flow diagrams visualize massive amounts of data from which you can gather quantitative and qualitative insights into past and present problems with your workflow stability—and where you should focus on making your processes more efficient.
In the Kanban methodology, Kanban boards are used to divide the workflow of a given project into three columns: “To Do” tasks, tasks that are “Work in Progress” (WIP), and tasks that are “Done.” Cumulative flow diagrams collect every task that has gone through your workflow to visualize three critical metrics:
Cycle time: This is the total time it takes your team to complete each task from the beginning to the end. One of the benefits of CFDs is that you can see where you can optimize your workflow to reduce cycle times.
Work in progress: This is the number of tasks your team is actively handling at a certain time. Cumulative flow diagrams will visualize inefficiencies in your project timeline when your team has too much or too little work in progress at any given point.
Throughput: This is the number of tasks your team can complete over a given period. As this is the ultimate measure of your team’s productivity, cumulative flow diagrams should show where you can align your efforts and resources so that throughput increases over time.
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Cumulative flow diagrams chart the number of tasks in each stage of your workflow at any given period along the process timeline. Tasks are depicted along the vertical axis, while the horizontal axis shows the process timeline.
The differently colored bands represent the respective stages of your workflow as they appear on the Kanban board. The bands should give you an idea of how many tasks are at each stage of the process at any given time and should go up or sideways proportionate to the number of tasks going through each stage.
The top line of each band shows the point at which each task arrives at the respective stages of your Kanban board, while the bottom line shows when they leave. The distance between the two should be consistent with maintaining a steady workflow.
In the above example, you can see the amount of work in progress at any given time, represented by the vertical distance between the “Done” and “To Do” bands. Higher WIP bands mean there’s more work in progress.
The “Done” column is represented at the bottom of the graph, visualizing the amount of work your team delivers in a given period. The slope of the band between two points will show your team’s average throughput.
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Given that the goal is a stable, predictable workflow, the ideal cumulative flow diagram should depict your task bands rising in parallel over time, with the “Done” band consistently growing taller. If the cumulative flow diagram shows a stable throughput, with new tasks entering steadily as more tasks leave, the next phase of optimization will be shortening the cycle times of your assignments.
If the bands widen too quickly, the number of tasks entering a certain stage of the Kanban board exceeds the outgoing number. In other words, your team has more tasks arriving than it can complete in a given period. With too much work in progress, your project will face a bottleneck. To avoid delays in task delivery and decreased throughput, you should focus more on completing tasks in progress before starting new ones.
Alternatively, if a band on your cumulative flow narrows sharply, the departure rate of the stage represented is higher than the arrival rate. This means you have more capacity than you need at this stage and should reallocate accordingly.
When done correctly, you should easily identify from your cumulative flow diagram the stability of your workflow and any problem areas to address. Correct analysis and monitoring of your cumulative flow diagram will tell you which areas need your attention to maintain continuous process improvement. As such, cumulative flow diagrams provide you the tools to improve the overall productivity and efficiency of your team and your projects.