# Determine The Percentage Rate Of Change In A Trendline

Feb 13, 2009I'm trying to determine the percentage rate of change in a trendline. I've got a sales chart with 90 days worth of sales figures. I can see that the trendline is trending down, but I'm not sure exactly how much.

If you take the first data point in a trendline and subtract it from the last data point and then divide that by the first it should give you the percent change. Excel must be able to do that math for you but I can't even figure it out to save my life. I can't even figure out how to display the first and last data point much less the "rate" of change I'm looking for.