In Excel, you can add trendlines to your charts that display a trend implied by the charted data. Trendlines are often added to XY (scatter) charts that correlate two different sets of numerical data to graphically point out the correlation between the two sets.

To add a trendline to your chart, choose Chart, Add Trendline on the Excel menu bar (note that the Chart menu appears on the regular Excel menu bar only when you select an embedded chart). This action opens the Add Trendline dialog box. Here, you can choose the type of trend in the Trend/Regression Type section (Linear, being the most common, is the default) and the data series on which to base the trend in the Based on Series list box.