﻿ FORECAST function

# FORECAST function

This article describes the formula syntax and usage of the FORECASTfunction in Microsoft Excel.

## Description

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)

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.

## 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.

How do I copy an example?

Important   Do not select the row or column headers.

Selecting an example from Help

2. Press CTRL+C.

3. In Excel, create a blank workbook or worksheet.

4. In the worksheet, select cell A1, and press CTRL+V.

Important   For the example to work properly, you must paste it into cell A1 of the worksheet.

5. 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.

After you copy the example to a blank worksheet, you can adapt it to suit your needs.

 1 2 3 4 5 6 7 8
 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 2010, Excel Starter, Excel Online, SharePoint Online

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