Syntax
FORECAST(x, known_y, known_x)
| Parameter | Description |
|---|---|
| x | Parameter of the FORECAST function. |
| known_y | Parameter of the FORECAST function. |
| known_x | Parameter of the FORECAST function. |
Examples
Next month's sales
Formula
=FORECAST(13, B2:B13, A2:A13)
Predicts month 13's sales based on the linear trend in months 1-12. If sales grew steadily, this extrapolates the line forward.
Expected cost at volume
Formula
=FORECAST(1000, C2:C20, D2:D20)
Predicts the total cost when producing 1,000 units, based on the observed cost-vs-volume relationship.
Interpolation
Formula
=FORECAST(5.5, B2:B11, A2:A11)
Estimates the value at x=5.5 even though your data only has integer x-values. FORECAST interpolates using the regression line.
Common Errors
#N/A
The known_y and known_x arrays have different lengths.
#DIV/0!
All x-values are identical (zero variance). The regression line is undefined.
Tips
Equivalent to SLOPE*x + INTERCEPT
FORECAST(x, y, x_known) = SLOPE(y, x_known)*x + INTERCEPT(y, x_known). It is a convenience function that combines both.
Only linear predictions
FORECAST assumes a straight-line relationship. If your data curves (exponential growth, seasonality), consider using LOGEST or time series methods instead.
Check RSQ before trusting results
If RSQ is low (below 0.5), the linear model is a poor fit and FORECAST predictions will be unreliable. Always validate the model first.
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