How To Extend a Trendline in Excel (Plus Types of Trendlines)

Updated June 30, 2022

There are many ways that businesses may gain useful points of data, whether through performance metrics, sales data or warehousing systems. Management can use this data not only to monitor current performance but also to forecast future values. Learning more about how to follow your data in Excel and use trendlines to forecast values can help you predict the performance of your teams and company. In this article, we explore what a trendline is, types of trendlines available to you in Excel, why you extend trendlines in Excel and how to extend a trendline in Excel.

Related: How To Make a Graph in Excel

What is a trendline in Excel?

A trendline is a line added to a data set to help illustrate the trend analysis in a series of data. Businesses use trendlines during data analysis to forecast future values and predict upcoming trends in particular data sets. A trendline visually enhances a chart and makes the analysis process easier for any person to understand. Trendlines are compatible for use in the following chart types:

Scattered chart
Bar chart
Column chart
Line chart
Stock chart
Bubble chart

You can't add trendlines to 3-D charts, stacked charts, radar charts or pie charts.

Related: How To Calculate NPV in Excel

Types of trendlines in Excel

There are many types of Excel trendlines you can use for extended data analysis. It's possible to add more than one trendline on a set of data to gain additional types of analysis. What type of trendline you use is often determined by the type of data you're tracking. Following is a list of common types of Excel trendlines:

Linear trendline

A linear trendline is a straight line that's used for steady increases or decreases in a set of data. You can identify a linear trendline if the pattern resembles a straight line. You can also add complexity through positive and negative values to get a more comprehensive and inclusive view.

Logarithmic trendline

A logarithmic trendline is a curved line that's used when the data increases or decreases rapidly prior to stabilizing. This type of trendline can show additional context to data analysis for businesses in all sectors. As with the linear trendline, you can also add positive or negative values to give additional information and context.

Polynomial trendline

A polynomial trendline is a curved line used to illustrate data fluctuation. It's best used in sets of data for analyzing gains and losses. The polynomial order shows by the number of bends that appear in the curve.

Power trendline

A power trendline is a curved line that compares measurements that increase at a specific rate. An excellent example of this would be the acceleration of a car at one-second intervals. This trendline isn't efficient for use if the data uses zero or negative values.

Exponential trendline

An exponential trendline is a curved line that's useful when the data rises at a steady or increasing rate. As with power trendlines, you can't use this trendline with zero or negative values. You can use this for instances of a consistent lower trend found in analysis.

Moving average trendline

A moving average trendline may show a pattern or trend more clearly. Moving average trendlines do this by using specific data points and averaging them, then using the averaged value as a point in the trendline. The period option sets the number of data points for this type of trendline.

Why extend a trendline in Excel?

Extending a trendline is a feature in Excel that allows you to set the trendline past the current set of data. Extending the trendline enables you to review trends and forecast how future values might affect the current data set. This can help create more accurate and comprehensive analyses, especially when dealing with fluctuating variables over time.

How to add and format your trendline in Excel

A trendline can be a helpful tool for analyzing sets of data. You can use multiple trendlines on one table, depending on your needs. To add a trendline to a data set, simply:

Select the data table to which you'd like to add a trendline.
In the corner of the data set, select the "+" icon.
Select the box next to the trendline of your choice.

Trendlines default to appear as a dashed line. If you use multiple trendlines or need to make the trendline stand out in the graphic, you can choose an alternate format for your trendline. To format your trendline:

Right-click your trendline and select "Format Trendline."
Click the "Fill and Line" category.
Select and customize your trendline with different colors, widths or dash types.

How to extend a trendline in Excel

If you want to extend the trendline on your data set to review what the data might show upon further analysis, you may consider extending your trendline. Use these six steps to extend your trendline:

Open your data set and right-click your trendline.
Select "Format Trendline" from the menu options.
Navigate to the "Forecast" section under "Trendline Options."
Type a value of your choice in the "Forward" box to extend your line forward.
Alternatively, type a value of your choice in the "Backward" box to extend your line backward.
Close the "Format Trendline" menu and continue analyzing your data.

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FAQ: All about trendlines in Excel

Learning to extend your trendline in Excel can help you provide advanced data analysis in any sector. Below, we've listed several questions and answers about using, analyzing and extending trendlines in Excel:

Why are trendlines important in Excel?

Trendlines are helpful for the visual processing and presentation of data. They can help forecast values based on your current data and give a clear picture of the future. They are widely used for more strategic and complex business processes, such as analysis and projection planning.

What is an R-squared value in a data set?

The R-squared value is a number from zero to one that reveals how close the estimated values for the trendline correspond to your data. The closer the value is to one, the more accurate your data is. If you're having trouble getting your R-squared value close to one, consider your raw data and evaluate it for accuracy.

What is data extrapolation?

Extrapolation is a method of mathematics that helps someone predict information beyond known data through programming and expanding their known data sets. In Excel, it's a type of data analysis and visualization that often makes use of trendlines. The user can calculate data to project future data movements on visible trendlines while also observing trends in current data.