Laneboard Cumulative Flow

What it is for

A cumulative flow diagram (CFD) shows, day by day, how many cards were in each list of a kanban board. Stacked on top of each other, the bands tell a story at a glance: whether work arrives faster than it gets finished, where cards pile up and whether the board is stable.

This tool replays the history of every card in a board file — a Laneboard project or board, a share snapshot or a Trello JSON export — and returns the chart as SVG, the daily numbers as a table and CSV, and a few summary numbers. The Laneboard app draws the same chart under Statistics.

It needs history: cards only appear from the day they were created, and moves that were never recorded cannot be shown. A period is limited to 366 days.

Worked example

The first example takes the Sprint board template from 2026-11-10 to 2026-11-24. The tool returns:

From 2026-11-10 to 2026-11-24, 14 cards arrived on Sprint 14 and 5 finished, with 4.6 cards in progress on average.

The metrics show 15 days, 14 arrivals, 5 finished cards, an average work in progress of 4.6 cards (the lists Ready, In progress and Review), 0.333 cards finished per day and a lead time by Little’s law of 13.8 days. In the daily table you can follow the sprint: on 2026-11-14 seven cards still sat in Backlog and three in In progress; by 2026-11-24 Done held five.

The third example uses a Trello export in October. Its archived list Parking lot still appears in the chart (one card spent time there), but work in progress counts only Doing, and finished means Done: 6 arrivals, 2 finished, average WIP 1.95.

How to read the result

• The chart — the last list (finished) is at the bottom, the first list on top. The top edge is everything that arrived; the bottom band grows with every finished card.
• Band height — how much work waits in that list. A band that keeps widening is a bottleneck; parallel edges mean a steady flow.
• Arrived / Finished — new cards and cards that entered the last open list in the period.
• Average work in progress — the mean number of cards between the first and last open list.
• Lead time by Little’s law — average WIP divided by cards finished per day. It is an estimate for a stable system, not a measurement; the statistics tool measures real lead times.
• Downloads — the SVG for slides or reports, the CSV for your own charts.

Tips and common mistakes

• Pick a period of at least two weeks; a few days rarely show a trend.
• Leave From empty to start at the first card (at most 90 days back); leave To empty to end at As of.
• Flat top edge, rising bottom: you are finishing more than you start — good before a release.
• If nothing moved into the last list, the tool warns and gives no Little’s law estimate (it would be a division by zero).
• Archived lists stay in the chart while they held cards, but never count as “in progress” or “finished”.
• Very large jumps in one day often mean many cards were imported or moved at once, not a change in flow.

FAQ

What is a cumulative flow diagram used for?

To see whether work is flowing: arrivals versus finished work, where it piles up, and how much is in progress over time. It is a standard chart in the Kanban method.

Why is the finished band at the bottom?

Finished cards only ever grow, so placing them at the bottom keeps the other bands readable and makes the slope of the finished line show throughput directly.

Does it work with Trello boards?

Yes. Upload the Trello JSON export. Trello keeps only the latest 1000 actions in the export, so older moves can be missing.

Is Little’s law exact?

Only for a stable process where arrivals and departures balance over the period. Treat it as a cross-check against the measured lead times.