Cumulative Flow Diagrams
The most powerful visualization for understanding system health at a glance.
1What Is a CFD?
A Cumulative Flow Diagram (CFD) is a stacked area chart showing how many items have reached each stage over time.
- X-axis: Time
- Y-axis: Cumulative count of items
- Each area: A workflow stage (usually colored differently)
How to read it:
The vertical distance between two lines is the number of items between those stages (WIP in those columns).
The horizontal distance between two lines is the approximate lead time through those stages.
A CFD that looks like smoothly flowing bands is a healthy system. One with bulging "bubbles" or flat lines has problems.
2Reading a Healthy CFD
Signs of healthy flow:
- Parallel bands: Lines move roughly parallel, meaning WIP is stable
- Consistent slope: The "Done" line rises at a steady rate (stable throughput)
- Narrow bands: WIP is limited, not excessive
- Smooth lines: No sudden drops or spikes
What the shape tells you:
- Narrow bands = low WIP = short lead times
- Wide bands = high WIP = long lead times
- Steeper "Done" line = higher throughput
- Flatter "Done" line = lower throughput
A glance at a healthy CFD shows: "Work flows smoothly, at consistent pace, with controlled WIP."
3Spotting Problems in a CFD
Problem 1: Widening bands (growing WIP)
- A stage's band gets thicker over time
- Means: Items entering faster than leaving
- Action: Stop starting, help finish
Problem 2: Flat lines (stalled stage)
- A line stops rising (or rises very slowly)
- Means: Nothing is completing in that stage
- Action: Investigate the blocker
Problem 3: Bulging "bubble"
- A band suddenly widens then narrows
- Means: A batch of work got stuck then released
- Action: Prevent batching, improve flow
Problem 4: Converging lines
- The gap between stages shrinks
- Means: WIP is being reduced (which may be good or indicate slowdown)
- Action: Depends on context—check why
Problem 5: Stepped "Done" line
- "Done" rises in occasional jumps instead of smoothly
- Means: Work is released in batches, not continuously
- Action: Enable more frequent releases
Bands are roughly parallel. The 'Done' line rises steadily at about 7 items per week. No bulges or flat spots. WIP looks consistent around 15 items.
The 'In Development' band widens steadily over three weeks. 'Done' line barely rises. Work is piling up in dev and nothing is completing.
4Using CFDs for Conversations
CFDs are excellent communication tools:
In standups: "Looking at the CFD, our 'Ready for QA' band has doubled this week. QA is becoming a bottleneck. Who can help?"
In retros: "This bulge in the CFD happened when we did the big release. Next time, let's release incrementally to avoid the batch."
With stakeholders: "Here's our flow over the last month. The steady rise in the Done line shows we're delivering consistently. Lead time has been stable at about 2 weeks."
For forecasting: "Our throughput has been 6-8 items per week. With 20 items in the backlog, we'll likely complete them in 3-4 weeks."
The key: CFDs make abstract flow concepts visible and concrete. They turn "I feel like we're behind" into "I can see WIP growing in code review."
Put your CFD on a wall or share it in a recurring Slack update. Visibility drives awareness. A CFD nobody looks at doesn't help.
- CFDs show cumulative items in each stage over time
- Vertical distance = WIP; Horizontal distance = lead time
- Healthy CFDs have parallel bands and steady slopes
- Bulges, flat spots, and widening bands indicate problems
- CFDs are communication tools, not just reports