The Excel LOGEST function fits an exponential curve y = b·m^x to your data and returns the array of its coefficients — the base m and the constant b. It is the exponential counterpart of LINEST.
Syntax
| Argument | Description | |
|---|---|---|
known_ys | Required | The dependent y-values. All must be positive. |
known_xs | Optional | The independent x-value(s). Omit to use {1,2,3,...}. Multiple columns fit a multi-variable exponential model. |
const | Optional | TRUE (or omitted) calculates b normally; FALSE forces b = 1. |
stats | Optional | TRUE returns additional regression statistics; FALSE or omitted returns only the coefficients. |
How to use it
LOGEST is an array formula. For one x-variable it returns a 1×2 array {m, b} describing the fitted curve y = b·m^x — the base comes first, the constant second.
Internally LOGEST runs a linear regression on the logarithms of the y-values, so every y must be positive — a zero or negative value returns #NUM!. Set stats to TRUE for R² and standard errors, just like LINEST.
Coefficients vs predictions: LOGEST gives you the curve's equation; GROWTH uses that same fit to return predicted y-values for new x's. Use LOGEST to read m and b; use GROWTH to forecast.
Try it: interactive demo
Pick a LOGEST example to see the formula and its result.
Practice workbook
Frequently asked questions
What does LOGEST return?
stats set to TRUE it adds R², standard errors and other regression statistics.How is LOGEST different from LINEST?
Why does LOGEST return #NUM!?
#NUM!.What is the relationship between LOGEST and GROWTH?
GROWTH applies that same curve to predict y-values for new x's. One gives the equation, the other gives forecasts.Master functions like this in one day
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