Apart from visually inspecting the graph, is there a way of calculating when a trend line will cross another series?

Is there a way to find the point of intersection of a trend line and another series on a chart in Excel? The other series may be another trend line or just the interpolated line drawn by Excel.

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I do not understand what "trendline will cross another series" means. – Toc May 24 '10 at 13:32
A Trendline can be added to a series - basically a prediction of the data extended beyond the known data. I want to know exactly when the trendline will intersect another series or even another trendline. – Adrian May 24 '10 at 14:20

Get equations for both trendlines. Put them in the form `y = f(x)`. Set them equal to each other. Solve for `x`.

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Is the equation available as an object then? - Excel calculates the trendline. – Adrian May 24 '10 at 10:18
For my current use - its just easier to look at the chart! - – Adrian May 27 '10 at 9:51

You would have to compute the slope of the line vs. every data point that you are looking at. Any data point that has a higher X axis value than the corresponding computed point on the slope would exceed it. You could optimize the search for this point by first computing your slope, then sorting your data points from the highest X axis value, in decending order, then interating through the list of data points and computing the corresponding X axis value of the trendline slope vs. the examined X axis value of the data point.

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