The Excel Forecast function predicts a future point on a linear trend line fitted to a supplied set of x- and y- values.
The syntax of the function is:
Where the arguments are as follows:
|x||-||A numeric x-value for which you want to forecast a new y-value.|
|known_y's||-||An array of known y-values.|
|known_x's||-||known_x's array should be the same length as known_y's, and the variance of the known_x's must not be zero.Note that the length of the|
In the spreadsheet below, the Excel Forecast function is used to predict an additional point along the straight line of best fit through a set of known x- and y-values (stored in cells F2:F7 and G2:G7).
As shown in cell F7 of the spreadsheet, the function to calculate the forecast y-value at x=7 is:
Further examples of the Excel Forecast function are provided on the Microsoft Office website
If you get an error from the Forecast function, this is likely to be one of the following:
|#N/A||-||Occurs if there are problems with the supplied known_x's or known_y's arrays - i.e. if either of these arrays is empty, or if the arrays are of different lengths.|
|#DIV/0!||-||Occurs if the variance of the supplied known_x's is equal to zero.|
|#VALUE!||-||Occurs if the supplied future value of x is non-numeric.|