Trend Line Equation and Coefficient of Determination To change the line properties, select the trend line and choose Format - Format Selection - Line. The trend line has the same color as the corresponding data series. Its name can be defined in options of the trend line. The basic idea is - using actual date serial numbers in a regression has the potential to create overflow errors, so you need to do something to avoid those overflows.A trend line is shown in the legend automatically. x space, then wait until the very end to perform the final exponentiation. One solution, as you've already discovered, is to transform dates from the actual serial number to 'days since a recent start date'.Īnother solution is to perform all the calculations in log(y) vs. Anytime you have a number like 44000 (your date values) in the exponent, you have the potential for some massive (or tiny) numbers - easily extending beyond what Excel can handle. The basic exponential equation that the chart trendline uses is y=b*exp(mx) (or, equivalently, as the LOGEST() function does it, y=b*m^x). I don't know exactly how microsoft has it programmed under the hood, but I strongly suspect that, yes, this is an accuracy/precision problem inside of the chart trendline calculations. Or, should I just shift the dates down to Maso that the date values range from 61 to 106? Is there some minimum date domain time period you need to specify to get this to work, or should I just delete the regular axis labels and add my own text string for the dates? Is this an accuracy/precision problem with the internal exponential trendline calculations? In other charts in the past I have been able to use dates along the x-axis, but these dates spanned a longer period, from 1940 to the present (date code numbers from 14612 to 43890) If I switch the domain values for the dates to numbers from 1 to 45, the exponential trend line plots just fine. There are no zero or negative values in the range, so the exponential trend line selection is not greyed out.īut nothing happens when I add an exponential trend line. The range is from 75 to 33,500 (as of today). The domain runs from Mainto April, so the numbers that represent the dates run from 43891 to 43935. I'm trying to plot coronavirus data against time and add an exponential trend line.

Excel exponential trendline equation