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|
An array of known x-values.Note that the length of the 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.
The spreadsheet below shows an example of the Forecast function used to predict an additional point along the straight line of best fit through the known_x's and known_y's in cells F2:F7 and G2:G7. These known points are shown in the graph on the same spreadsheet.
The above example gives the result 32.666667.
Further examples of the Excel Forecast function can be found on the Microsoft Office website
If your Forecast function gives you an error message, use the table below to look up the likely cause:
|#VALUE!||-||Produced if the supplied future x value is non-numeric|
|#NA||-||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!||-||Produced if the variance of the supplied known_x's evaluates to zero.|