- Identify the starting and ending points of the trendline. For example, if your trendline is based on monthly sales data, you might use the first and last months of the data set.
- Plug the x-values (i.e., the time periods) for the starting and ending points into the equation for the trendline. For example, if the starting point is January and the ending point is December, you would plug in 1 for x in the equation for January and 12 for x in the equation for December.
- Calculate the y-values (i.e., the sales figures) for the starting and ending points using the trendline equation. For example, if the equation for January is y = 2.1973(1) + 3211.2, the sales figure for January would be 3213.4 (rounded to the nearest tenth).
- Calculate the percent increase between the starting and ending points using the following formula:
Percent increase = ((Ending value - Starting value) / Starting value) x 100
For example, if the sales figure for January was 3213.4 and the sales figure for December was 3300.0, the percent increase would be:
((3300.0 - 3213.4) / 3213.4) x 100 = 2.7%
So in this case, the trendline suggests that there was a 2.7% increase in sales over the course of the year. Keep in mind that this calculation assumes that the trendline accurately represents the underlying data and that there are no other factors influencing the sales figures.