# 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.

## 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 (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.

## 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 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.