CFD: read the cumulative flow diagram
A CFD is not report decoration: it is an X-ray of the flow. Toggle between a healthy scenario, a bottleneck and too much WIP and practice the three readings (WIP, throughput and lead time) right on the shape.
Cumulative Flow Diagram (CFD)
The three bands rise thin and almost parallel. The vertical gap between them stays small and steady: about 16 items in the system at once. The horizontal gap is short too, a lead time of roughly 13 days. The green delivery line rises almost glued to the arrival line, finishing close to 6 items per week: it leaves at the same pace it enters.
This is what healthy flow looks like. In a CFD the vertical gap between bands is WIP and the horizontal gap is lead time. When the bands stay thin and parallel, work in progress is under control and each item crosses the system fast, without sitting in a queue.
On a real board, this is the team that only pulls a new card when it finishes another. Work enters and leaves at the same beat, deliveries are frequent, and each item’s lead time is predictable.
The call here is to protect what works: keep the WIP limit where it is and watch whether any band starts to thicken. This is not the moment to pile on more work just because there seems to be slack.
The three readings of this shape
Switch scenarios and read the diagram: the shape tells the story of the flow.
What a CFD is
The Cumulative Flow Diagram (CFD) stacks, over time, how many items have arrived, have started and have finished. Each colored band is a state of the flow; the total height at an instant is all the work that has entered the system so far.
Because the curves are cumulative, they never go down, they only get steeper or flatter. The information lives in the shape of the bands (parallel, widening, flattening): a CFD turns three flow measures into a single figure you read at a glance.
The three readings: WIP, throughput and lead time
The first reading is the vertical gap between the bands = WIP: on a given day, the distance from the “arrived” curve to the “delivered” curve is how much work sits in the system. The second is the slope of the top band = arrival rate / throughput: parallel bands mean work goes in and out at the same pace; widening bands mean the exit cannot keep up with the entry.
The third is the horizontal distance, at the same height, between “arrived” and “delivered” = lead time approximately: how long, on average, an item takes from arrival to delivery. Three flow questions (how much, how fast, how long) answered by a single chart.
Warning signs in a CFD
Bands that widen over time signal a bottleneck: work enters a stage faster than it leaves, so WIP and lead time grow together. A band that goes flat (almost no slope) reveals an idle or starving stage: capacity sitting still, waiting for work to arrive.
A healthy CFD has thin, parallel bands rising at a steady pace: stable WIP, short and predictable lead time. Once you can read this figure, a single glance tells you where the flow is hurting.
Frequently asked questions about CFDs
What is a CFD (Cumulative Flow Diagram)?
It is a chart that stacks, over time, how many items have arrived, started and finished. Each band is a state of the flow, and the shape of the bands reveals WIP, throughput and lead time at once.
How do I read WIP in a CFD?
WIP is the vertical gap between the bands: on a given day, the distance from the “arrived” curve to the “delivered” curve shows how much work is in the system. The taller the column, the more work in progress.
How does a CFD show lead time?
Through the horizontal distance, at the same height, between the arrival and delivery curves. It approximates how long an item takes from arrival to delivery, no need to time each item.
What CFD shape indicates a bottleneck?
Bands that widen over time: work enters faster than it leaves, so WIP and lead time grow together. Thin, parallel bands indicate healthy flow.
Enjoyed learning by doing?
Watch the CFD react to your decisions: manage a squad in the Kanban Game.
