Add a trend or moving average line to a chart Add a Trendline Select a chart. Select the + to the top right of the chart. Select Trendline. Format a trendline In the Format Trendline pane, select a Trendline Option to choose the trendline you want for your chart. Formatting a trendline is a statistical way to measure data: Set a value in the Forward and Backward fields to project your data into the future. Source: Microsoft