FORECAST function: Description, Usage, Syntax, Examples and Explanation

What is FORECAST function in Excel?

FORECAST function is one of Statistical functions in Microsoft Excel that 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.
Worked Example:   Forecast vs Trend Function in Excel

Syntax of FORECAST function

FORECAST(x, known_y’s, known_x’s)

The FORECAST function syntax has the following arguments:

  • 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.

FORECAST formula explanation

  • 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:Equationand:


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

Example of FORECAST function

Steps to follow:

1. Open a new Excel worksheet.

2. Copy data in the following table below and paste it in cell A1

Note: For formulas to show results, select them, press F2 key on your keyboard and then press Enter.

You can adjust the column widths to see all the data, if need be.

Known Y Known X
6 20
7 28
9 31
15 38
21 40
Formula Description Result
=FORECAST(30,A2:A6,B2:B6) Predicts a value for y given an x value of 30 10.607253

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