Trendlines

**jtj10003** · 02-13-2009, 08:29 PM

Hey All, I'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. Any help would be great. Thanks.

**shg** · 02-13-2009, 08:54 PM

You can display the equation of the trendline on the chart (right-click the trendline) if you just want a glance at the slope, or you can get the parameters using LINEST.

**jtj10003** · 02-16-2009, 11:50 AM

Thanks for the response but what I'm looking for is a percentage value. If I had a hypothetical sales history of $100 on Monday and $90 on Tuesday then my sales would be trending down at 10%. I'm just looking for a way for excel to give me that 10% number when I have 90 days worth of sales trend analysis as opposed to two.

**shg** · 02-16-2009, 12:16 PM

Post a workbook and I'll show you.

**jtj10003** · 02-16-2009, 04:52 PM

Thanks again. I'm sure I'm missing something easy. Here's and example workbook. It shows a down trend line. The question is what percentage is the downward trend?

**shg** · 02-16-2009, 04:59 PM

You can read it right off the trendline formula. The slope is -0.986, so the trendline trends down by (1 - 0.986) or 1.4% per period.

If the slope were, say, 1.1, then it would be trending up by 10% per period. Capische?

To see that same value (the 0.986) in a cell, =LINEST(H14:H25).