# FORECAST

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.

Syntax

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

X     is the data point for which you want to predict a value.

Known_y's     is the dependent array or range of data.

Known_x's     is the independent array or range of data.

Remarks

• 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:

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

Example

The example may be easier to understand if you copy it to a blank worksheet.

• Create a blank workbook or worksheet.
• Select the example in the Help topic.

Note   Do not select the row or column headers.

Selecting an example from Help
• Press CTRL+C.
• In the worksheet, select cell A1, and press CTRL+V.
• To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.
A B
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 (10.60725)

Applies to:
Excel 2003