basic

First-Order Reaction Half-Life Calculator

t½ = ln 2 / k — half-life from the rate constant.

Calculates the half-life of a first-order chemical reaction from the rate constant, and the concentration remaining after any elapsed time.

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

Inputs

Results

Enter values and click Calculate to see results.
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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; [A]t = [A]₀ × e^(−kt)

In depth

Calculates the half-life of a first-order chemical reaction from the rate constant, and the concentration remaining after any elapsed time.