Combo chart: definition, examples, and best practices.

What is a combo chart?

A combo chart, also called a dual-axis chart or combination chart, mixes chart geometries on a shared category axis. Bars often carry a volume measure. A line on a secondary axis carries a rate, margin or conversion percentage. The point is to show how the two move together without forcing them onto one misleading scale.

Dual axes can invent correlations if the scales are stretched. Label both axes clearly, and never use the secondary axis to manufacture a story that is not in the data.

A worked example

Monthly active users rise across twelve months while conversion rate dips.

When to use a combo chart

• Plotting units or revenue as bars against margin or conversion as a line
• Showing traffic volume next to bounce rate or attach rate
• Pairing headcount with revenue per FTE across periods
• Any board slide where volume and rate must appear in one frame

When not to use it

• When both measures share units and a single axis is clearer, use a clustered bar or line chart
• When you need a cumulative bridge of drivers, use a waterfall

How to read it

Read bars against the primary axis and the line against the secondary axis. Ask whether the scales make the relationship look stronger than it is.

Best practices

• Label both axes explicitly, including units
• Never use a secondary axis to manufacture a correlation
• Keep the line weight at least 3px so it stays visible over bars
• Limit the chart to one bar series and one line series when possible
• Call out the crossover or divergence in a short annotation if that is the point of the slide