Definition
Cumulative Flow Diagram
A cumulative flow diagram (CFD) is a stacked area chart showing how many items sit in each workflow state over time. The colored bands reveal flow health at a glance: a widening band means work is piling up in that stage, a steady set of parallel bands means smooth flow. It is Kanban's richest single picture of a system's behavior.
Key takeaways
- A cumulative flow diagram (CFD) is a stacked area chart of how many items sit in each workflow state over time.
- A widening band is a bottleneck — work entering a stage faster than it leaves; steady parallel bands mean healthy flow.
- One CFD encodes WIP, throughput, and lead time at once: band thickness is WIP, and the gap between started and done approximates lead time.
- It turns vague impressions like 'review feels backed up' into evidence, and shows whether a process change actually helped.
A CFD plots time on the horizontal axis and cumulative item count on the vertical, with one stacked band per workflow state — backlog, in progress, in review, done. Because the bands stack, the total height is all the work in the system, and each band's thickness at any moment is how much work is currently in that state. Watching the bands evolve shows the whole system breathing.
Its diagnostic power is in the shapes. A band that widens over time is a bottleneck — work is entering a stage faster than it leaves. Bands that stay parallel and steady signal balanced, healthy flow. The vertical distance between the 'started' and 'done' bands is the approximate work in progress, and the horizontal distance between them approximates lead time — so a single chart encodes WIP, throughput, and lead time at once, connected by Little's Law.
Read regularly, a CFD turns vague impressions ('review feels backed up') into evidence, and shows whether a process change actually improved flow. It rewards the same discipline Kanban does: keep states meaningful, keep WIP bounded, and let the picture tell you where the constraint really is.
Related terms
- ThroughputThroughput is the number of work items a team completes in a given period — issues finished per week, for example. It is the simplest flow metric: a direct count of output over time. Tracked across periods, throughput reveals a team's real delivery capacity and is the basis for probabilistic, estimate-free forecasting.
- Cycle TimeCycle time is how long an issue takes from the moment work actively starts on it to the moment it is done. Measured in hours or days, it captures the team's hands-on flow efficiency. Shorter, more consistent cycle times mean a more predictable system — the core flow metric Kanban teams optimize.
- Lead TimeLead time is the total elapsed time from when an issue is first created or requested to when it is delivered. Unlike cycle time, it includes the waiting period in the backlog before work begins. Lead time reflects the customer's experience of how long a request actually takes end to end.
- Little's LawLittle's Law is a foundational result from queueing theory stating that, on average, the number of items in a system equals the rate items arrive (or complete) multiplied by the average time each spends in the system. For teams: average work in progress equals throughput times cycle time — which is why limiting WIP directly shortens cycle time.