What a trendline does and when you need one

A trendline is a line drawn through your data points that shows the overall direction they're moving. If you have sales numbers across twelve months, a trendline shows whether sales are generally going up, down, or staying flat — even if individual months bounce around. Google Sheets can draw this line for you automatically and calculate the math behind it.

You use a trendline when you want to see the pattern underneath noisy data. Monthly website traffic might jump around day to day, but a trendline shows the real trend. It's useful for presentations because it makes a pattern visible at a glance, and it's useful for planning because you can extend the line forward to estimate what comes next.

Key Takeaways

  • Trendlines only work on scatter charts and line charts in Google Sheets, not on bar or column charts.
  • You add a trendline by clicking the chart, opening the chart editor, and selecting "Series" then "Trendline" from the menu.
  • Google Sheets offers four types of trendlines: linear (straight line), exponential (curved upward), polynomial (curved), and moving average (smooths out bumps).
  • You can display the equation and R-squared value on your chart so readers see how well the trendline fits your actual data.

Creating a chart that can hold a trendline

Before you add a trendline, you need a chart. Trendlines work only on scatter charts and line charts — not on bar charts, column charts, or pie charts. If you're starting from scratch, highlight your data (including headers), click "Insert" at the top, then "Chart". Google Sheets will suggest a chart type; if it suggests a bar or column chart, you'll need to change it.

In the chart editor panel that opens on the right, look for the "Chart type" dropdown near the top. Click it and select either "Scatter chart" or "Line chart". A scatter chart shows individual points; a line chart connects them. For most data, a scatter chart is clearer because you can see both the actual points and the trendline. Once you've chosen your chart type, you're ready to add the trendline.

Adding a trendline step by step

Click on your chart to select it. The chart editor panel will open on the right side. Near the top of that panel, you'll see tabs: "Setup", "Chart & axis titles", "Series", and "Customize". Click the "Series" tab.

In the Series tab, you'll see a list of your data series (usually just one). Click on the series name. Below it, a new set of options appears. Scroll down until you see "Trendline" — it's a checkbox with a dropdown next to it. Check the box to turn on the trendline. A straight line will appear on your chart when ready.

The dropdown next to "Trendline" lets you choose the type. "Linear" draws a straight line and works for most cases. "Exponential" curves upward and works for data that's accelerating. "Polynomial" creates a curved line that bends to fit your data more closely. "Moving average" smooths out short-term bumps to show the underlying pattern. Start with linear unless you have a reason to choose something else.

Showing the equation and fit on your chart

Once your trendline is visible, you can display two useful pieces of information: the equation of the line and the R-squared value. The equation tells you the exact formula (useful if you want to predict future values by hand). The R-squared value (ranging from 0 to 1) tells you how well the trendline fits your data — closer to 1 means the trendline matches your points closely; closer to 0 means the points scatter widely around the line.

In the Series tab where you turned on the trendline, look for checkboxes labeled "Show equation" and "Show R²". Check both if you want them visible on the chart. The equation will appear as text on the chart (for example, "y = 2.5x + 10"), and the R² value will appear separately. You can move these labels by clicking and dragging them to a clearer spot on the chart.

Changing the trendline color and style

By default, Google Sheets colors your trendline the same as your data series. If you want it to stand out, you can change its color and thickness. In the Series tab, look for "Trendline color" — click the color box to choose a different color. You might make it darker, brighter, or a contrasting color so readers notice it.

Just below that, you'll find "Trendline opacity" (how transparent it is) and sometimes "Trendline width" (how thick the line is). A thicker line (3 to 4 pixels) makes the trend more obvious in a presentation. Lower opacity (50 to 70 percent) lets the data points show through without the trendline overwhelming them. Experiment with these settings until the chart looks clear.

When a trendline doesn't fit your data well

If your R² value is below 0.5, your trendline is not capturing the pattern in your data — the points are too scattered. This doesn't mean you've done something wrong; it means the relationship isn't a straightforward straight line. You have a few options: try a different trendline type (polynomial often fits messy data better), check whether you have outliers that are throwing off the line, or accept that the data straightforward doesn't follow a clear pattern.

Outliers are extreme values that don't fit the rest of your data. If you have one month with unusually high sales, it can pull the trendline in that direction. You can't delete outliers just to make the trendline look better, but you can note them in your presentation and explain why they're unusual. Sometimes the story in your data is "mostly steady growth, except for this one spike" — and that's worth saying.

Using the trendline to predict future values

Once you have a trendline with an equation visible, you can use it to estimate what comes next. If your equation says "y = 2.5x + 10" and your last data point is at x = 12, you can calculate the next value: y = 2.5(13) + 10 = 42.5. This is a rough estimate, not a may provide, but it's useful for planning.

Google Sheets doesn't automatically extend the trendline into the future for you, but you can do it by hand. In the Series tab, look for "Forecast period" — some chart types let you enter a number of periods to extend the line forward. If that option isn't available, you can calculate future points using the equation and plot them as new data points on your chart.

Frequently Asked Questions

Can I add a trendline to a bar chart?

No. Trendlines only work on scatter and line charts. If you need to show a trend in bar chart data, convert it to a scatter or line chart first. You'll lose the bar appearance, but you'll gain the ability to add a trendline.

What does R² mean and what's a good value?

R² tells you how much of your data's variation the trendline explains. An R² of 0.8 or higher means the trendline fits well. Below 0.5 means the trendline doesn't capture the pattern. There's no universal "good" value — it depends on your field and what you're trying to show.

Can I have more than one trendline on the same chart?

If you have multiple data series (multiple lines or sets of points), you can add a separate trendline to each one. Click each series in the Series tab and add a trendline to it individually. Each trendline will use its own color.

What's the difference between polynomial and moving average trendlines?

Polynomial creates a curved line that bends to fit your data more closely. Moving average smooths out short-term bumps by averaging groups of points. Use polynomial if you think your data follows a curved pattern; use moving average if you want to see the underlying trend without the noise.

How do I remove a trendline?

Click your chart, go to the Series tab in the chart editor, click your data series, and uncheck the "Trendline" box. The line disappears when ready.