# Excel FORECAST.LINEAR Function

The Excel FORECAST function predicts a value based on existing values along a linear trend. FORECAST calculates future value predictions using linear regression, and can be used to predict numeric values like sales, inventory, expenses, measurements, etc.

*Note: Starting with Excel 2016, the FORECAST function was replaced with the FORECAST.LINEAR function. Microsoft recommends replacing FORECAST with FORECAST.LINEAR, since FORECAST will eventually be deprecated.*

*x*- The x value data point to use to calculate a prediction.*known_ys*- The dependent array or range of data (y values).*kown_xs*- The independent array or range of data (x values).

The FORECAST.LINEAR function predicts a value based on existing values along a linear trend. FORECAST.LINEAR calculates future value predictions using linear regression, and can be used to predict numeric values like sales, inventory, test scores, expenses, measurements, etc.

*Note: Starting with Excel 2016, the FORECAST function was replaced with the FORECAST.LINEAR function. Microsoft recommends replacing FORECAST with FORECAST.LINEAR, since FORECAST will eventually be deprecated.*

In statistics, linear regression is an approach for modeling the relationship between a dependent variable (y values) and an independent variable (x values). FORECAST.LINEAR uses this approach to calculate a y value for a given x value based on existing x and y values. In other words, for a given value x, FORECAST.LINEAR returns a predicted value based on the linear regression relationship between x values and y values.

### Example

In the example shown above, the formula in cell D13 is:

=FORECAST.LINEAR(B13,sales,periods)

where **sales** (C5:C12) and **periods** (B5:B12) are named ranges. With these inputs, the FORECAST.LINEAR function returns 1505.36 in cell D13. As the formula is copied down the table, FORECAST.LINEAR returns predicted values in D13:D16, using values in column B for x.

The chart to the right shows this data plotted in a scatter plot.

*Note: Although FORECAST calculates future value predictions, it can also be used to interpolate and even predict the past. Mark at Excel Off The Grid has a detailed explanation here.*

### Notes

- If
*x*is not numeric, FORECAST.LINEAR returns a #VALUE! error. - If
*known_ys*and*known_xs*are not the same size, FORECAST.LINEAR will #N/A. - If the variance of
*known_x*values is zero, FORECAST.LINEAR will return #DIV/0!.

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