How to Show an Opening-to-Closing Bridge in a Sankey Diagram
Draw a balance that moves from opening to closing as a Sankey: put the start and everything added into one pool, then split it into the end figure and the losses. Worked example.
A bridge shows how a quantity changed over a period: where it started, what was added, what was lost and where it ended. In a Sankey you draw it with a single pool in the middle, so every addition and every loss sits at the same scale.
The example follows the number of customer accounts over one month. 1,000 accounts at the start plus 150 new and 20 won back make a pool of 1,170. The pool then splits into 1,090 accounts at the end, 70 cancelled and 10 merged into other accounts.
The method works for anything that carries over: revenue, headcount, stock, accounts, cash. The MRR movement and failed payment recovery templates use the same idea.
Use one pool, not a line from start to end
It is tempting to draw a ribbon from the opening balance straight to the closing balance and hang the additions and losses off it. That makes the additions look as if they come from nowhere and the losses as if they leave from nowhere.
A pool node fixes it: everything that was available during the period flows in, and everything that happened to it flows out. The editor then checks the balance for you, because what enters the pool must equal what leaves.
Four steps
- Choose one period and one unit, and use the closing figure of the last period as the opening figure of this one.
- Add the opening balance and every addition as flows into the pool.
- Add the closing balance and every loss as flows out of the pool.
- Check that both sides of the pool add up. If not, a movement is missing, and it is better to add a node called Other adjustments than to hide the gap.
Explaining a loss
A bridge answers how much changed. A second level answers why. Split a loss node into its causes, such as cancelled by the customer and failed payment in the MRR movement template, and the reader can see what drove it.
Do not split every node. The more nodes there are, the thinner the small ribbons become, and the pool stops being easy to read.
When a waterfall is better
A waterfall chart reads exact amounts more easily and works for a bridge with a handful of steps. A Sankey is the better choice when you want to see proportions between additions and losses, or to break a loss into causes. Many teams use both: the waterfall for the number, the Sankey for the explanation.
Key points
- 1,170 accounts are in the pool: 1,000 at the start, 150 new and 20 won back.
- 1,090 accounts remain at the end, a net increase of 90 (9%) over the start.
- Cancellations (70) are 6% of the pool and are the only sizeable loss.
- The figures are invented.
The example’s data
Invented account counts for illustration. Not data about any real business.
| From | To | Amount (accounts) |
|---|---|---|
| Accounts at start | Accounts in the month | 1000 |
| New accounts | Accounts in the month | 150 |
| Won back | Accounts in the month | 20 |
| Accounts in the month | Accounts at end | 1090 |
| Accounts in the month | Cancelled | 70 |
| Accounts in the month | Merged | 10 |
The same data as CSV
source,target,value
Accounts at start,Accounts in the month,1000
New accounts,Accounts in the month,150
Won back,Accounts in the month,20
Accounts in the month,Accounts at end,1090
Accounts in the month,Cancelled,70
Accounts in the month,Merged,10How it works
Put the opening balance and every addition in one pool
One flow per addition, all into a single node.
Split the pool into the closing balance and the losses
One flow per loss, plus one for the closing balance.
Check that the pool balances
In must equal out. Add an Other adjustments node if a movement is missing, so the gap is visible.
Frequently asked questions
Can the bridge cover several periods?
Chain them: the closing node of one period is the opening node of the next. Keep the unit and the node names the same so the ribbons can be compared.
What if the closing balance is smaller than the opening one?
Nothing changes in the method. The losses are simply wider than the additions, and the closing ribbon is narrower than the opening one.
Open this bridge and change a number
Open the example as your own chart and change an amount to see the pool rebalance.