Half-Life & Radioactive Decay Calculator
Remaining quantity, elapsed time or half-life for exponential decay (radioactive isotopes, drugs, first-order reactions).
How to use the Half-Life & Radioactive Decay Calculator
- Enter or select: Initial amount N₀.
- Fill in what you know of: Remaining amount N, Elapsed time, Half-life t½ — leave the unknown empty.
- The results (Remaining amount, Elapsed time, Half-life, Decay constant λ, Mean lifetime τ, Remaining) are calculated instantly as you type.
- Use “Copy link” to share the calculation with the same input values.
Formula
- N = N₀ · (½)^(t/t½)
- λ = ln2 / t½
About this tool
Use the same time unit for elapsed time and half-life.