I once spent way too long trying to cram both revenue (in the tens of thousands) and profit margin (a small percentage) onto a single bar chart. The margin line was basically invisible next to the towering revenue bars. That frustration is exactly what combo charts were built to solve, and once I learned how to use them properly, they became one of my go-to chart types for any report involving two different units of measurement.
What Is a Combo Chart?
A combo chart (short for combination chart) lets you display two or more chart types — like columns and lines — on the same chart, often using two different vertical axes. The classic example is a bar chart showing revenue alongside a line chart showing profit margin percentage, plotted on a secondary axis so both are readable despite having wildly different scales.
Combo charts are perfect any time you have two related but differently-scaled metrics that you want your audience to compare in a single glance.
When Should You Use a Combo Chart?
I reach for combo charts when:
- I’m comparing two metrics with very different scales (e.g., units sold vs. revenue)
- I want to show a trend line over a set of bar values (e.g., monthly sales bars with a rolling average line)
- I need to highlight a target or threshold against actual performance
- One dataset is best shown as discrete values (bars) and another as continuous change (line)
If both your metrics share a similar scale, you probably don’t need a secondary axis — a simple grouped bar chart might communicate the comparison more clearly.
Required Data Structure
You just need your data organized in standard tabular form, with a category column and two or more numeric columns. Here’s an example:
| Month | Revenue | Profit Margin % |
|---|---|---|
| Jan | 45000 | 12 |
| Feb | 48000 | 14 |
| Mar | 52000 | 11 |
| Apr | 61000 | 16 |
| May | 58000 | 15 |
Notice how Revenue is in the tens of thousands and Profit Margin is a small percentage — this is exactly the kind of mismatch a combo chart is designed to handle.
Step-by-Step Instructions
Here’s exactly how I build one:
- Select your full data range, including headers.
- Go to the Insert tab.
- In the Charts group, click Insert Combo Chart (the icon looks like overlapping bar and line shapes).
- Choose one of the built-in combos, such as Clustered Column – Line on Secondary Axis, or select Create Custom Combo Chart for full control.
- In the Custom Combo Chart dialog, choose a chart type for each data series individually (e.g., set Revenue to Clustered Column, Profit Margin to Line), and check the Secondary Axis box next to the series that needs its own scale.
- Click OK, and Excel builds the combo chart.
Formatting and Settings I Adjust
Once the chart is generated, here’s what I typically refine:
- Secondary axis formatting: Right-click the secondary axis and format its number format to match the data (e.g., percentage format for margin).
- Line styling: I usually thicken the line and add markers (Format Data Series > Marker Options) so it stands out clearly against the bars.
- Color contrast: Bars and lines should use visually distinct colors — I avoid using similar shades that make it hard to tell the series apart.
- Legend placement: With two series types, a clear legend at the bottom or right becomes essential — I always double check it’s visible and correctly labeled.
A Practical Example
Say I’m reporting on a retail store’s monthly performance. I plot Revenue as columns and Profit Margin as a line on the secondary axis. Instantly, the audience sees that even though April had the highest revenue, March actually had a revenue increase but a dip in margin — a nuance that would be completely lost if I’d only shown one metric at a time. That’s the real power of a combo chart: it lets two stories be told in one glance without misleading scale comparisons.
Common Mistakes to Avoid
Here’s what I watch out for:
- Forgetting the secondary axis: If you skip this step, your line series with small percentage values will look like a flat line hugging the bottom of the chart, dwarfed by bar values in the thousands.
- Using too many series: Combo charts work best with two, maybe three, series. Beyond that, the chart becomes cluttered and hard to interpret.
- Mismatched axis scales confusing viewers: Always label both axes clearly so no one mistakes which scale belongs to which series.
- Choosing the wrong chart type per series: Discrete comparisons (like monthly totals) usually work better as bars, while trends over time usually work better as lines. Mixing these thoughtfully — not randomly — makes the chart more effective.
Troubleshooting Tips
If your combo chart isn’t behaving:
- Line series is invisible or flat: Check that it’s assigned to the secondary axis under Format Data Series > Series Options.
- “Create Custom Combo Chart” option missing: This feature requires Excel 2013 or later; older versions require manually changing individual series chart types.
- Colors are hard to distinguish: Manually recolor each series under Format Data Series > Fill for more contrast.
- Data labels overlapping between series: Turn off labels for one series, or reposition them (e.g., line labels above the line, bar labels centered inside the bar).
Real-World Use Cases
I’ve built combo charts for:
- Comparing sales volume (bars) against year-over-year growth rate (line)
- Showing website traffic (bars) alongside conversion rate (line)
- Displaying actual vs. target performance, with actuals as bars and a flat target line overlaid
- Visualizing temperature (line) against rainfall (bars) in a weather report
Best Practices
Before finalizing a combo chart, I always confirm:
- Each series uses the chart type that best fits its nature (bars for discrete totals, lines for trends)
- The secondary axis is clearly labeled with correct units
- Colors are distinct enough to read at a glance, even in black-and-white printouts
- The chart isn’t overloaded with more than two or three series
- A brief title or subtitle clarifies exactly what’s being compared
Combo charts solve a problem that plain charts simply can’t — comparing metrics on different scales without one drowning out the other. Once you get comfortable assigning chart types and axes per series, you’ll find yourself reaching for combo charts constantly, especially in any report where you’re telling two related stories at once.