Trendlines are useful for revealing patterns or trends in your data. They are mostly used in XY scatter charts but are also useful in line, area, and bar charts. To add a trendline to your chart, follow these instructions…
1. Select the chart.
2. Select the series you wish to use to create the trendline.
3. Go to Chart Tools, select the Layout tab and click Trendlines.
4. Select the type of relationship you are expecting the data to reveal, your choices are Linear, Exponential, Linear Forecast, or Two Period Moving Average. You can also select More Trendline Options to reveal even more types.
5. Right-click the newly created trendline and select Format Trendline. Use the Line Color, Line Style and Shadow sections to modify the look of the trendline.
6. Click Close.