How to read a Sankey diagram
A Sankey diagram has two ingredients. Nodes are the bars or boxes that stand for a source, a destination or a stop along the way, such as gross pay, take-home pay or housing. Links are the bands between them, and a band’s width is proportional to the amount it carries, so a $30,000 band is twice as wide as a $15,000 one. Money usually flows from left to right.
One rule makes the chart trustworthy: what flows into a node equals what flows out. If a household spends more than it earns, the gap appears as another source, such as money drawn from savings or new debt, rather than vanishing. When you read any Sankey, check:
- The period: one month, one year or a lifetime total.
- The units: dollars, percentages, or future versus today’s dollars.
- Which bands are transfers, such as moving cash into an investment account, rather than spending.
- Whether small flows were grouped into “other,” which can hide detail.
What a household cash flow Sankey shows
Most budgets start from take-home pay, which hides a large share of what a household earns. A cash flow Sankey starts from gross income and shows every layer: pre-tax deductions such as 401(k) deferrals and health premiums, payroll taxes, federal and state income tax, and finally take-home pay splitting into housing, food, transportation, debt payments and saving.
Seen this way, a few things become obvious. Taxes are often one of the widest bands, which is why tax planning can matter as much as trimming small expenses. Saving shows up in two places, before and after tax, and the two together give your true savings rate. The diagram also changes shape in retirement: wages disappear from the left side and are replaced by Social Security, pensions and account withdrawals, including required minimum distributions from pre-tax accounts, each of which can carry its own tax band.
How to build a cash flow Sankey
You can draw one from a pay stub, last year’s tax return and a year of bank and card statements. Most charting tools that support Sankey diagrams take a simple table with three columns: where the money comes from, where it goes, and how much. A year is usually the right period, because it captures irregular bills such as insurance premiums, property taxes and holiday spending that a single month misses. Build the table in layers so each node balances:
- Start with each gross income source: salary, bonus, side income, interest and dividends.
- Subtract pre-tax deductions, then payroll and income taxes, to reach take-home pay.
- Split take-home pay into spending categories and after-tax saving.
- Add a balancing flow: a surplus into savings, or a shortfall drawn from savings or debt.
- Check that the right side adds up to the left before trusting the picture.
Sankey diagram vs. other ways to chart money
A Sankey answers “where did the money go?” for a single period better than any other chart, but it is weak at showing change over time. A diagram of this year says nothing about whether spending is creeping up or saving is falling. Pair it with a year-by-year chart of cash flow and net worth, and use a budget to act on what the Sankey reveals. For future years, the same picture can be drawn from a financial projection instead of past statements.
It also struggles in a few situations. Dozens of small categories turn into slivers too thin to read, so group minor items. Transfers between your own accounts can be mistaken for spending. And because every band must have a positive width, a loss such as a falling portfolio value does not fit naturally: a Sankey shows flows of cash, not changes in the value of what you own.
Illustrative numbers
A $120,000 salary drawn as a Sankey (single filer, 2026)
- Gross pay
- Wages before any deduction
- Pre-tax deductions
- 401(k) deferrals, health premiums and other amounts taken before income tax
- Payroll tax
- Social Security and Medicare tax (FICA)
- Income tax
- Federal, state and local income tax
At every node of a Sankey, money in equals money out.
Gross salary$120,000
Pre-tax 401(k) deferral$10,000
Social Security and Medicare tax (7.65%)$9,180
Federal income tax on $93,900 of taxable income$15,370
Take-home pay$85,450
Housing, food and other spending$70,000
Left to save after tax$15,450
Drawn to scale, the two tax bands carry $24,550, about 20% of the salary, almost as much as the two saving bands, which carry $25,450, about 21%. The figures use the 2026 brackets, the $16,100 standard deduction and a state with no state income tax on wages, such as Tennessee or New Hampshire.
At a glance
Which chart answers which money question
| Chart | Best for | Weak spot |
|---|---|---|
| Sankey diagram | Where one period’s money came from and went | Hides change over time; tiny flows become slivers |
| Stacked bar chart | How income and spending shift year to year | Hard to trace one dollar’s path |
| Pie chart | One set of shares, such as a spending split | One level only; no sources or destinations |
| Waterfall chart | Stepping from gross pay down to what is left | Grows long with many categories |
| Line chart | Balances and net worth over time | Shows totals, not the flows between them |
Put it in your plan
Sankey Diagram in MoneyWhatIf
On the Projection page, choose Cash flow in the chart picker, click a year to pin it, and turn on Flow: that year is drawn as a money-flow diagram tracing its sources into taxes, housing, living costs, investments and remaining cash. With Flow on, the CSV download holds that year’s sources and destinations. The Estate page has its own Sankey diagram, which spends the gross estate down through debts, taxes, costs and giving to what beneficiaries receive; Summary draws one ribbon per asset category and Detailed one per asset.
Common questions
Sankey Diagram FAQs
Why is it called a Sankey diagram?
It is named after Captain Matthew Henry Phineas Riall Sankey, an Irish engineer who used the format in 1898 to show energy flowing through a steam engine and how much was lost along the way. Earlier flow maps existed, most famously Charles Minard’s 1869 chart of Napoleon’s Russian campaign, but Sankey’s name stuck.
What are Sankey diagrams used for?
They show any flow whose total is conserved, so that everything going in comes out somewhere. The format began in engineering, where it still maps energy and heat losses; Lawrence Livermore National Laboratory, for example, publishes yearly charts of US energy flows in this style. Sankeys also trace materials through supply chains, water use, and people moving through a website or a hiring process. In finance they show a company’s revenue splitting into costs and profit, or a household’s income splitting into taxes, spending and saving.
Can a Sankey diagram show negative cash flow?
Not as a negative band, because a band cannot have negative width. A deficit is drawn as an extra source on the left, labeled something like “drawn from savings” or “added to credit card debt,” so the two sides still balance. That makes a shortfall year easy to spot: a new band appears feeding spending from something other than income.
Should a Sankey show monthly or annual cash flow?
Annual is usually clearer for planning. Many costs arrive once or twice a year, such as insurance premiums, property taxes, tuition and bonuses, and a single month can make them vanish or look enormous. A monthly Sankey works for day-to-day expenses, ideally averaged over several months. Whatever you choose, keep every band in the same period.
What is the difference between a Sankey diagram and an alluvial diagram?
Both draw bands between columns, but they answer different questions. A Sankey follows a quantity, such as dollars or energy, through a network of sources and uses, and its flows can merge, split or skip a stage. An alluvial diagram tracks how the same group is sorted into categories at several points, such as households moving between tax brackets from one year to the next, so every column holds the same total. For one year of household cash flow, a Sankey is the better fit.