# Linear trendline equation incorrect in Excel

I'm using Microsoft Office Excel 2007 for some statistics work for school. I made a linear trendline on a graph corresponding to a data set. This is what it looks like: The data set in question is 4pcmm. All looks well.

However, the equation of the trendline is off. For example, if we calculate it at an X position of 50:

y = (4538.1 * 50) + (1 * 10^6)

Punch this into Excel (or just a calculator) and we get 1,226,905. However the graph clearly shows that at 50, the line is above 1,600,000. Hell, the line never even goes below 1,400,000.

So what's going on? Have I screwed something up or is it Excel which is at fault? And how do I fix this?

• I think it has to do with the constant you are adding. If you look at the graph, the constant should be 1.45e+06. If you want to check, use SLOPE() and INTERCEPT() on the data. – LDC3 Nov 5 '14 at 4:54
• This is the second recent question I've seen with Excel reporting incorrect trendline parameters. Up until then, I had never seen a case. I wonder if something like a recent Microsoft update introduced some type of corruption. – fixer1234 Nov 5 '14 at 5:07
• @LDC3: I can't really use SLOPE() or INTERCEPT() because I don't have a data set of the points of the line itself. The trendline was made using "Add Trendline" on the 4pcmm data set. – puggsoy Nov 5 '14 at 6:16
• @fixer1234: Yeah, I've done this before with other data sets and it worked perfectly. I don't remember updating Excel recently, though. – puggsoy Nov 5 '14 at 6:16
• @puggsoy, `INTERCEPT` gives you the y-intercept of the trend line not the first data point. – Mr. Mascaro Nov 5 '14 at 16:37