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Statistical function

LOGEST

Returns the parameters of an exponential curve fitted to data, as an array.

Rarely usedDifficulty 1550 · AdvancedUsage rank #447 of 520
Practice · 2 questions →

When to use it

Fits an exponential curve y = b × m^x and returns m and b, with optional statistics like LINEST.

The shape of it

Syntax
=LOGEST(known_y's, [known_x's], [const], [stats])

Worked examples

  • A doubling series

    =LOGEST({100,200,400},{1,2,3}) → {2,50}

    Doubling each period: m = 2, and b = 50 makes y = 100 at x = 1.

  • Growth rate

    =INDEX(LOGEST(B2:B13,A2:A13),1)-1 → 0.041

    The monthly growth rate implied by the fit.

  • Fit quality

    =INDEX(LOGEST(B2:B13,A2:A13,TRUE,TRUE),3,1) → 0.97

    R² of the fit on log scale.

Worth knowing

  • GROWTH uses the same fit to predict values.
  • The R² is on LN(y), not y.
  • Coefficients come back right to left like LINEST.

Where it goes wrong

  • #NUM! when any y is zero or negative.
  • #REF! when x and y differ in length.

Related

AVERAGECOUNTCOUNTACOUNTIFCOUNTIFSMAX

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