Interactive graph, is it possible

Yes! Interactive graphs are not only possible but preferable in scenarios when excessive chart elements make them ineffective. As I can best understand very recent video tutorials viewed on this subject, IA graphs rely on action items like radio buttons, etc. Check out a few by copy/pasting verbatim titles below into your browser, since admins won't let me post a link yet. Then, let me know whatcha think!

Create your first interactive chart in Excel in under 5 minutes

MrExcel's Learn Excel #776 - Interactive Chart

Excel Dynamic Chart with Drop down List (column graph with average line)

I agree that dynamic charts are possible. However, I would approach the task you describe without using a chart at all:

1) Perform regression on the data. All of the equations used by Excel chart trendline can be made linear, so I would use the LINEST() function to perform the regression https://support.office.com/en-us/art...a-fa7abf772b6d
2) With the regressed parameters, solve the equation for the endpoints.

I can then use a chart to visualize the results, but I would not use the chart as a tool on the way to getting the results.

Mr. Shorty,

I thought the entire purpose of an interactive chart is to omit an element for best overall clarity but display it in proper context when needed. Is this not correct?

CluckeyJD: You may be correct that many people think of that when they think of an interactive chart. In this case, the OP seems to be describing that he/she wants to interact in a specific way with a chart trendline. I have found that I much prefer interacting with trendlines directly in the spreadsheet rather than the chart.

MrShorty: I didn't comprehend the OPer's request for methods to redraw a trendline. But it's easy to see why this can lend high value to any data visualization chart. So, please let me know what you think of techniques on the YT video link below. They rely on a scroll bar over a line chart but may be a great start for broader application in the OPer's scenario. See: youtu.be/m-C4a0Em3i0

@CluckeyJD: What I see in this youtube video is essentially the same kind of thing as I suggested to the OP -- Interact with the spreadsheet and then the chart will reflect the changes in the spreadsheet. In this latest youtube video, notice that the user interacts directly with D5. The slider form control that the youtuber uses is directly changing the value of D5. The spreadsheet then responds to the changes in D5, and the chart reflects those changes to the spreadsheet. Most of the "interactive chart" techniques that I know of use the same kind of philosophy -- have the user interact directly with the spreadsheet (though the user may not realize they are interacting with the spreadsheet because I used form controls and/or hidden columns/rows/cells), and then the chart reflects those changes in the spreadsheet.