To add a trendline to your Excel chart or graph, right-click on the data series and go to ‘Add Trendline’. You will be met with the following options:
These are curved trendlines useful when your chart is demonstrating growth at increasing rates. For example, the growth of computer processing power has continued at an exponential rate for many years now.
A linear trendline is a straight line to indicate the line of best fit. These are useful when demonstrating something which is growing at a steady continuous rate. Your data set can be described as linear if the data points resemble a line rather than wavering up and down. For example this chart, showing units sold by month.
Logarithmic trendlines should be used to trend a data set which has seen a sudden shift that has then levelled out to become the norm. In this example, units sold have exploded from June following a successful advertising campaign.
Polynomial Trendlines are curved and good for trending data sets which fluctuate up and down. E.g. a company share price.
A power trendline is a curved line useful when your dataset is growing at an increasing rate. In this example, the company’s share price is growing by 150% every year.
A moving average trendline smoothes out any outliers in your data by showing the overall average at each data point on the timeline. You can set the Period at any number from 2 onwards, a Period of 2 will begin the trendline from the second data point. If you use a Period of 2, the average of points 1 and 2 is used for the second point on the trendline, the age of 2 and 3 is used for the third point, 3 and 4 for the fourth, etc, etc..