Quick Answer

FORECAST Function

Predicts a y-value from a linear regression at a given x.

Syntax

FORECAST

(x, known_ys, known_xs)

Parameters

Parameter	Description	Required
x	The x-value at which to predict the corresponding y-value.	Required
known_ys	The dependent (y) values of the known data used to fit the line.	Required
known_xs	The independent (x) values of the known data; must match the size of known_ys.	Required

Basic Example

Predict the next value on a rising trend

=FORECAST(6,{2,3,5,7,11},{1,2,3,4,5})

Result12.2

The fitted line is y = -1 + 2.2x, so at x=6 the prediction is -1 + 2.2*6 = 12.2.

Advanced Examples

Example 1: Forecast from worksheet ranges

Project next month's revenue

Use a column of past revenues and a column of period numbers

=FORECAST(13,B2:B12,A2:A12)

Result: Predicted revenue for period 13

Least-squares line through the 11 points is extended to x=13.

Example 2: Equivalence to FORECAST.LINEAR

Legacy vs modern name

Both return the same prediction

=FORECAST(6,{2,3,5,7,11},{1,2,3,4,5}) and =FORECAST.LINEAR(6,{2,3,5,7,11},{1,2,3,4,5})

Result: 12.2 for both

FORECAST.LINEAR is the renamed, recommended form of the legacy FORECAST.

How FORECAST Works

FORECAST fits a straight line y = a + bx by least squares, where the slope b = Σ((x - x̄)(y - ȳ)) / Σ(x - x̄)² and the intercept a = ȳ - b·x̄. It then evaluates that line at the supplied x. The prediction is purely linear and assumes the underlying relationship is roughly straight.

1

List known data

Place known x-values and known y-values in equal-length ranges.

2

Pick target x

Decide the x at which you want a prediction.

3

Enter formula

Type =FORECAST(x, known_ys, known_xs).

Important Notes & Limitations

Models only a linear relationship; curved trends need TREND/GROWTH or transforms.
known_xs and known_ys must have the same number of points, or #N/A is returned.
If the x-values have no variance (all equal), the function returns #DIV/0!.

Common Errors & Fixes

#N/Aknown_xs and known_ys have different sizes, or a non-numeric x was supplied.

Fix: Make the two arrays the same length and pass a numeric x.

#DIV/0!All known_xs values are identical, so the slope is undefined.

Fix: Provide x-values that actually vary.

Download Practice File

Practice FORECAST with Real Data

Download a sample CSV file with pre-populated data and practice exercises for the FORECAST function. Works in both Excel and Google Sheets.

Works in Google SheetsCompatible with ExcelIncludes exercises

File format: CSV (comma-separated values) - opens in Excel, Google Sheets, and all spreadsheet apps

Related Functions

AVERAGE

Calculates the mean of the provided numbers.

AVERAGEIF

Averages values that satisfy one condition.

AVERAGEIFS

Averages values that meet all of the specified conditions.

CORREL

Pearson correlation coefficient between two arrays.

COUNT

COUNT returns the count of cells containing numbers in a range.

COUNTA

COUNTA returns the count of all non-empty cells in a range, including text, numbers, and logical values.

Frequently Asked Questions

Is FORECAST the same as FORECAST.LINEAR?

Yes. FORECAST.LINEAR is the modern name; in current Excel they return the same value.

Can FORECAST predict backwards (x smaller than the data)?

Yes. It simply evaluates the fitted line at any x, including outside the original range.

How is this different from TREND?

FORECAST returns a single predicted y; TREND can return an entire array of predictions at once.