How to Add a Secondary Axis to a Chart in Microsoft Excel

Creating a chart in Excel is usually straightforward, but things get complicated when you try to compare two sets of data that use vastly different scales. For example, if you want to plot “Total Revenue in Dollars” against “Number of Website Visitors” on the same chart, the revenue might be $1,000,000 while the visitors are only 5,000. Because the primary Y-axis scales up to a million to accommodate the revenue, the visitor data will be crushed into a flat, unreadable line at the very bottom of the chart.

To fix this, you must add a “Secondary Axis.” This places a second set of numbers on the right-hand side of the chart specifically scaled to fit your smaller dataset, allowing both lines to be clearly visible and easily compared.

This guide explains how to add and format a secondary axis in Microsoft Excel.

Step 1: Create a Basic Chart

First, you must create a standard chart containing both sets of data, even if one dataset is currently unreadable.

1. Highlight the data you want to plot, including the column headers (e.g., Dates, Revenue, and Visitors).
2. Click the Insert tab on the Excel ribbon.
3. In the “Charts” group, click the Insert Line or Area Chart icon and select a basic 2D Line chart.

You will now see a chart where one line looks normal, and the other line is completely flat along the bottom.

Step 2: Add the Secondary Axis

Now, you must tell Excel to assign that flat line to a brand new axis on the right side of the screen.

1. Look closely at your chart and locate the “flat” line (your smaller dataset).
2. Right-click directly on the flat line itself. (If the line is too thin to click, right-click the legend entry for that data series instead).
3. From the pop-up menu, select Format Data Series…
4. A “Format Data Series” pane will slide out on the right side of your screen.
5. Look under the “Series Options” section (represented by an icon that looks like three tiny columns).
6. You will see a section labeled “Plot Series On”. By default, “Primary Axis” is selected.
7. Click the radio button next to Secondary Axis.

Instantly, a new set of numbers will appear on the right edge of your chart, and the previously flat line will jump up, revealing its actual trends and fluctuations.

Step 3: Change the Chart Type for Clarity (Optional but Recommended)

When you have two intersecting lines on a chart utilizing two different axes, it can confuse the audience. They might not know which line corresponds to which axis. To make the data instantly readable, it is highly recommended to change the chart type of one dataset (e.g., make Revenue a bar chart and keep Visitors as a line chart).

1. Right-click on either of the lines in your chart.
2. Select Change Series Chart Type… from the menu.
3. The “Change Chart Type” dialog box will appear. Look at the bottom half of the window, where your two data series are listed.
4. Change the “Chart Type” drop-down menu for your primary data (e.g., Revenue) to Clustered Column.
5. Leave the chart type for your secondary data (e.g., Visitors) as a Line.
6. Ensure the “Secondary Axis” checkbox is still checked for your secondary data.
7. Click OK.

You now have a clean, professional “Combo Chart.” The bars represent the numbers on the left axis, and the line represents the numbers on the right axis, making complex comparisons effortless for your audience to understand.