The natural logarithm, base e. It turns multiplicative growth into something additive, which is why it appears in doubling-time math, elasticity, and regression on growth data.

Syntax

=LN(number)

• Inverse of EXP

  =LN(EXP(2)) → 2

  LN undoes EXP.

• A plain log

  =LN(100) → 4.605170186

  Natural log of 100.

• Doubling time

  =LN(2)/LN(1.07) → 10.24476835

  Years for money to double at 7% a year.

• Log returns: =LN(price_today/price_yesterday) add up across periods, unlike percentage returns.
• LN of a ratio is a symmetric measure of change: LN(120/100) and LN(100/120) are equal and opposite.
• Fit an exponential trend by regressing LN(y) on x with SLOPE and INTERCEPT.

• #NUM! for zero or negative input.
• LN is base e; LOG10 is base 10. Mixing them changes results by a factor of 2.3026.