basic

First-Order Reaction Half-Life Calculator

t½ = ln 2 / k — independent of starting concentration.

Compute the half-life of a first-order reaction directly from its rate constant: t½ = ln 2 / k = 0.693 / k. The half-life of a true first-order process does not depend on initial concentration.

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

t½ = ln 2 / k

In depth

Compute the half-life of a first-order reaction directly from its rate constant: t½ = ln 2 / k = 0.693 / k. The half-life of a true first-order process does not depend on initial concentration.