What is a cumulative flow diagram?

A Cumulative Flow Diagram (CFD) is a stacked area chart that shows the number of items in each workflow stage over time. The X-axis is time; the Y-axis is total work items. Each stage is a colored band. The width of any band at a point in time represents the number of items in that stage. The vertical distance between two stages at a point in time represents the amount of WIP between them. Key insights from CFD: (1) Bottlenecks — a widening band indicates work accumulating (too much WIP, capacity constraint); (2) Cycle time — the horizontal distance between when an item enters the first stage and the last stage; (3) Throughput — the slope of the top line (items per time); (4) Ideal flow — smooth, parallel bands with steady slopes. Distortions reveal process problems: steep slopes indicate burst activity, horizontal plateaus indicate stoppage. CFDs are the primary flow metric tool in Kanban and complement burndown charts in Scrum teams using hybrid approaches.