Should the Axis Start at Zero? The Rule Is About the Mark, Not the Chart
The argument comes back every quarter. One person says an axis must always start at zero. Another says that makes half their charts useless. Both are describing real situations, and the rule that settles it is not about the chart type as a name. It is about what the ink encodes.
What you do: if the mark's length carries the value, the axis starts at zero. If the mark's position carries the value, it does not have to.
The short version. Bars from zero, always. Lines and dots, from wherever the data lives, clearly labelled.
Why bars are different
A bar is a rectangle whose length is the number. Two regions, 1,750 and 3,150. West is 1.8 times East, and on a zero-based axis a reader gets that ratio for free by looking.
Start the axis at 1,600 and the drawn bars become 150 and 1,550 units long. The reader's eye now reports a ratio above ten to one. Nobody misread the chart: the chart said ten to one, in the only language a bar has. That is why truncating a bar axis is not a matter of taste. The encoding is length, and the length is now wrong.
Why lines are different
A line encodes value as vertical position, and what the reader takes from it is the shape: the rises, the falls, the turning points. Nobody measures the distance from a line down to the axis.
Take an on-time delivery rate that runs 96.2, 96.8, 97.1, 95.4, 94.9, 95.2 percent over six months. That is a real fall of more than two points and worth a conversation. On a zero-based axis it is a flat line near the top of an empty chart, and the empty 94 percent below it is telling the reader nothing they did not already know.
Plot the same series from 94 to 98 and the drop in month four is visible, which is the entire reason for drawing it. The obligation that comes with the non-zero axis is labelling: real tick values, no hiding, and a subtitle that says what the range is if the audience is not close to the data.
The cases, in one table
| Chart | What encodes the value | Zero? | Note |
|---|---|---|---|
| Bar, column | Length | Always | No exceptions worth the argument |
| Stacked bar | Length, twice over | Always | The stack is meaningless otherwise |
| Line, time series | Position | Not required | Label the range, keep ticks real |
| Dot plot, lollipop | Position of the dot | Not required | The stick makes it length again, so beware |
| Area chart | Area, which is length | Always | Otherwise the fill is a lie |
| Scatter | Position on both axes | Not required | Zero often wastes the plot |
| Percent change | Position, with a real zero | Keep zero visible | Zero means no change, so it matters |
| Index, base 100 | Position | Show 100 | 100 is the reference line, not 0 |
Where the argument actually comes from
Both camps are defending something real. The zero camp is defending the reader who will glance at a chart for two seconds and take a ratio from it. The non-zero camp is defending the analyst who has a two-point move in a rate and no way to show it. Neither is being dishonest, and the way through is not a compromise; it is picking a mark whose encoding suits the data.
Small variation on a high base? Use a line or a dot, not a bar, and set the range to the data. Comparing magnitudes across categories? Use a bar, from zero. If you genuinely need both, draw two charts: the levels as bars from zero, and the change as its own chart. That is nearly always clearer than one chart trying to do both.
Doing it in Excel
- Click the vertical axis, then Format Axis, then Bounds. Minimum and Maximum are the two boxes.
- Type a round number, not the value Excel proposes. 94 reads as a decision; 94.37 reads as an accident.
- Set Major unit so the gridlines land on readable values.
- Leave the axis labels on. The single most common failure is a truncated axis with the numbers switched off for a cleaner look.
- Put the range in the subtitle for anyone seeing the chart in a screenshot, out of context, six weeks later. That is how most charts are eventually read.
How to apply this to your own work
- Find every bar chart in your standard pack and check the axis minimum. Any that is not zero is misstating a ratio right now.
- Find every line chart forced to zero and ask what it is hiding. Flat lines near the top of an empty chart are the tell.
- Where you truncate, write the range into the subtitle rather than relying on the axis labels alone.
- Convert any bar chart of small variation on a big base into a dot plot, and see how much easier it is to read.
- Screenshot one chart, crop the axis off, and show it to a colleague. What they say is what your chart says.
The one habit to keep
Say the sentence the chart makes a reader believe, then check the numbers support that exact sentence. "West is about ten times East" is a sentence a truncated bar chart makes people believe about a 1.8 times difference.
Where does the axis start on the chart at the front of your last deck?
Charts and Visualization is the chart-choosing book: what each shape can carry, what it quietly distorts, and how to label it so the reader reaches your finding without being told.
Charts and Visualization, $19 →How charts mislead works this and seven other distortions on one table, and chart design basics covers the rest of the formatting. Build steps are in the Excel Kit.
Read How Charts Mislead →