Half-Life Calculator

Radioactive decay — remaining quantity, elapsed time, or half-life.

Calculator Numbers & Math Updated Apr 20, 2026
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How to Use
  1. Enter any three of: initial amount, half-life, elapsed time, remaining.
  2. Leave the unknown blank to solve for it.
Input
Decay

Formulas

Remaining
N(t) = N₀ · (1/2)^(t/T½)
Decay constant
λ = ln(2) / T½ · N(t) = N₀ · e^(−λt)

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