What Is the FORECAST Function in Excel?
 Description
The FORECAST function is a Statistical function in Excel. It calculates or predicts a future value based on existing value. The existing values are known as xvalues and yvalues and the future value is predicted by using linear regression. For instance, you can predict future numeric values of sales, earnings and expenses, inventory, consumer trends, measurements, etc.
 Purpose
To predict or calculate a future value with a linear trend
 Syntax
=FORECAST(x, known_ys, known_xs)
 Arguments Description
Value  Required/Optional  Description 

x  Required  The value for which the future value to predict or calculate 
known_ys  Required  The dependent array or range of data (y values) 
known_xs  Required  The independent array or range of data (x values) 
 Return Value
A predicted or calculated value
FORECAST Functions in Excel: 5 Examples
Example 1 – FORECAST.LINEAR Function in Excel
FORECAST.LINEAR is formerly known as the FORECAST function in Excel. Microsoft replaced the FORECAST function with the FORECAST.LINEAR in 2016.
 Purpose
This function predicts the future value based on the existing set of values.
 Equation
y = a + bx
a = constant value, intercept, which follows,
And b = coefficient, the slope of the line, which follows,
Here,
means the Average value (arithmetic mean) of the sample value.
 Return Value
A calculated future value
Based on the above discussion, the FORECAST.LINEAR formula for our given dataset will be,
=FORECAST.LINEAR(B18,$C$5:$C$16,$B$5:$B$16)
Where,
B18 = The value for which the future value to predict or calculate
$C$5:$C$16 = The dependent array or range of data (y values)
$B$5:$B$16 = The independent array or range of data (x values)
Example 2 – FORECAST.ETS in Excel
The FORECAST.ETS function is used to calculate or predict future value based on existing values by using the AAA version of the Exponential Smoothing (ETS) algorithm.
AAA = Additive Error, Additive Trend, and Additive Seasonality.
ETS = Exponential Triple Smoothing algorithm.
This algorithm loosens up the insignificant deviations in data trends by detecting seasonality patterns and confidence intervals.
 Syntax
=FORECAST.ETS (target_date, values, timeline, [seasonality], [data_completion], [aggregation])
 Argument Description
Value  Required/Optional  Description 

target_date  Required  The timeline for the prediction should be calculated 
values  Required  Existing or historical value(yvalues), dependent array, or range of data from which a prediction will be calculated. 
timeline  Required  Numeric independent array or range of values (xvalues) 
[seasonality]  Optional 
Seasonality calculation.

[data_completion]  Optional 
Missing data calculation.

[aggregation]  Optional  Indicates which method to use. Default value is 0 = Average 
 Return Value
A calculation of the predicted value.
The FORECAST.ETS formula for our given dataset shown above will be,
=FORECAST.LINEAR(B18,$C$5:$C$16,$B$5:$B$16)
B18 = The value for which the future value to predict or calculate
$C$5:$C$16 = The dependent array or range of data (y values)
$B$5:$B$16 = The independent array or range of data (x values)
Read More: TREND vs FORECAST Function in Excel
Example 3 – The FORECAST.ETS.CONFINT
The FORECAST.ETS.CONFINT function returns a confidence interval (CI) for a forecast value at a specified timeline. A confidence level of 90% means the predicted values are expected to fall within this radius from the result of the FORECAST.ETS function produced.
 Syntax
=FORECAST.ETS.CONFINT (target_date, values, timeline, [confidence_level], [seasonality], [data_completion], [aggregation])
 Argument Description
Value  Required/Optional  Description 

target_date  Required  The timeline for the prediction should be calculated 
values  Required  Existing or historical value(yvalues), dependent array, or range of data from which a prediction will be calculated. 
timeline  Required  Numeric independent array or range of values (xvalues) 
[confidence_level]  Optional  The confidence level for the calculated confidence interval. A numeric value between 0 and 1 (exclusive). Default 0.95 or 95% 
[seasonality]  Optional  Seasonality calculation.

[data_completion]  Optional  Missing data calculation.

[aggregation]  Optional  Indicates which method to use. Default value is 0 = Average 
 Return Value
Confidence Interval (CI) value
The FORECAST.ETS.CONFINT formula for our given dataset will be:
=FORECAST.ETS.CONFINT(E5,$C$5:$C$16,$B$5:$B$16,G5)
E5 = The value for which the future value to predict or calculate
$C$5:$C$16 = The dependent array or range of data (y values)
$B$5:$B$16 = The independent array or range of data (x values)
G5 = Confidence level
Example 4 – FORECAST.ETS.SEASONALITY
The FORECAST.ETS.SEASONALITY function is used to return the length of a repetitive pattern in a specified timeline.
 Syntax
=FORECAST.ETS.SEASONALITY (values, timeline, [data_completion], [aggregation])
 Argument Description
Value  Required/Optional  Description 

values  Required  Existing or historical value(yvalues), dependent array, or range of data from which a prediction will be calculated. 
timeline  Required  Numeric independent array or range of values (xvalues) 
[data_completion]  Optional  Missing data calculation.

[aggregation]  Optional  Indicates which method to use. Default value is 0 = Average 
 Return Value
Season length in a specified timeline
The FORECAST.ETS.SEASONALITY formula for our given dataset shown above will be,
=FORECAST.ETS.SEASONALITY($C$5:$C$16,$B$5:$B$16)
$C$5:$C$16 = The dependent array or range of data (Score column as y values)
$B$5:$B$16 = The independent array or range of data (ID column as x values)
Example 5 – FORECAST.ETS.STAT in Excel
The FORECAST.ETS.STAT function returns a statistical value relating to the time series forecasting with the FORECAST.ETS function.
Syntax
=FORECAST.ETS.STAT (values, timeline, statistic_type, [seasonality], [data_completion], [aggregation])
 Argument Description
Value  Required/Optional  Description 

values  Required  Existing or historical value(yvalues), dependent array, or range of data from which a prediction will be calculated. 
timeline  Required  Numeric independent array or range of values (xvalues) 
statistic_type  Required  The type of statistical value to return.

[seasonality]  Optional  Seasonality calculation.

[data_completion]  Optional  Missing data calculation.

[aggregation]  Optional  Indicates which method to use. Default value is 0 = Average 
 Return Value
A statistical result
The formula for the FORECAST.ETS.STAT function with different statistic types is shown in the picture below,
=FORECAST.ETS.SEASONALITY($C$5:$C$16,$B$5:$B$16,1)
$C$5:$C$16 = The dependent array or range of data (Score column as y values)
$B$5:$B$16 = The independent array or range of data (ID column as x values)
1 = Alpha statistic type (this numeric argument can be anything from 1 to 8 based on the requirement)
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Excel FORECAST Function: Knowledge Hub
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