FORECAST function

This article describes the formula syntax and usage of the FORECAST function (function: A prewritten formula that takes a value or values, performs an operation, and returns a value or values. Use functions to simplify and shorten formulas on a worksheet, especially those that perform lengthy or complex calculations.) in Microsoft Excel.


Calculates, or predicts, a future value by using existing values. The predicted value is a y-value for a given x-value. The known values are existing x-values and y-values, and the new value is predicted by using linear regression. You can use this function to predict future sales, inventory requirements, or consumer trends.


FORECAST(x, known_y's, known_x's)

The FORECAST function syntax has the following arguments (argument: A value that provides information to an action, an event, a method, a property, a function, or a procedure.):

  • X    Required. The data point for which you want to predict a value.
  • Known_y's    Required. The dependent array or range of data.
  • Known_x's    Required. The independent array or range of data.


  • If x is nonnumeric, FORECAST returns the #VALUE! error value.
  • If known_y's and known_x's are empty or contain a different number of data points, FORECAST returns the #N/A error value.
  • If the variance of known_x's equals zero, then FORECAST returns the #DIV/0! error value.
  • The equation for FORECAST is a+bx, where:




and where x and y are the sample means AVERAGE(known_x's) and AVERAGE(known y's).


The workbook below shows examples of this function. Inspect them, change existing formulas, or enter your own formulas to learn how the function works.

To work more in-depth with the example data in Excel, download the embedded workbook to your computer, and then open it in Excel.

Applies to:
Excel 2013, Excel Online