# Forecast Excel worksheet function

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 Excel function to predict future sales, inventory requirements, consumer trends or weight loss!.
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).
The Excel training video demonstrates the concept.

Description of the forecast function in Excel

Microsoft Excel Training Videos