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Excel FORECAST function

The FORECAST function predicts a future value based on existing values by using the linear regression.

FORECAST function VS. FORECAST.LINEAR function

Starting from Excel 2016, the FORECAST function has been replaced by the FORECAST.LINEAR function. Although they can both be used to predict a future value based on given values, the FORECAST.LINEAR function is more recommended for future use, because the FORECAST function will eventually be deprecated in future versions of Excel.

Syntax

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

Arguments

  • x (required): The data point (x value) for which you want to predict a y value;
  • known_y’s (required): The dependent array or range of y values;
  • known_x’s (required): The independent array or range of x values.

Remarks

1. The #VALUE! error occurs if x is nonnumeric;
2. The #N/A error occurs if known_y’s and know_x’s arrays are not the same size;
3. The #DIV/0! error occurs if the variance of know_x’s equals to zero;
4. The equation for the FORECAST function is:
y = a + bx
where

and

and and are the averages of know_x’s and known_y’s.

Return value

It returns a numeric value.

Example

As shown in the table below, there is a list of monthly sales from January to August, to predict the sales along the linear trend for the next few months, you can try the FORECAST function as follows.

1. Firstly, you need to create a helper column (the FORECASE column in this case).

Tips: Creating a helper column helps to distinguish the predicted values from the actual values in a chart using different colors, which makes the chart more intuitive.

2. Find the cell containing the last sales (C13 in this case) in the Sales column, select a cell (D13) next to it in the helper column, and then enter a number that is the same as the last sales.

3. Select the cell (D14), copy or enter the formula below and press the Enter key to get the result. Then select the result cell and drag its AutoFill Handle down to get other predicted values.

=FORECAST(B14,$C$6:$C$13,$B$6:$B$13)

Then you can create a forecast chart based on the table data as shown in the screenshot below.

Related Functions

Excel FORECAST.ETS function
The FORECAST.ETS function uses the Exponential Smoothing (ETS) algorithm to predict a future value based on a series of existing values.

Excel FORECAST.ETS.CONFINT function
The FORECAST.ETS.CONFINT function calculates the confidence interval for the forecast value at the specified target date.

Excel FORECAST.ETS.SEASONALITY function
The FORECAST.ETS.SEASONALITY function returns the length of a seasonal pattern based on existing values and a timeline.

Excel FORECAST.ETS.STAT function
The FORECAST.ETS.STAT function returns a specified statistical value as a result of time series forecasting.

Excel FORECAST.LINEAR function
The FORECAST.LINEAR function predicts a future value based on existing values by using the linear regression.


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