☢️ Half-Life Calculator (Radioactive Decay)
Work with exponential decay: enter three of initial amount, remaining amount, elapsed time and half-life to find the fourth.
Elapsed time (t)
11460 time
Radioactive decay: N = N₀ · (½)^(t / t½). Use the same time unit for t and the half-life. 🔒 Computed in your browser.
How the half-life calculator (radioactive decay) works
Radioactive decay follows N = N₀ · (½)^(t/t½), where N₀ is the initial amount, N the amount remaining after time t, and t½ the half-life. Enter any three and the tool solves for the fourth; keep the elapsed time and half-life in the same unit.
From carbon-14 dating to dosimetry: after one half-life, half remains; after two, a quarter; after n, (½)ⁿ. Works for any first-order decay, not just nuclear.
Frequently asked questions
What is a half-life?
The time for half of a decaying substance to be gone. After each half-life the amount halves: 100 → 50 → 25 → 12.5, and so on.
How do I calculate how much remains?
N = N₀ · (½)^(t/t½). Enter the initial amount, elapsed time and half-life (same time unit for both), and the tool gives what remains.
How do I find the age from remaining amount?
Solve for t: t = t½ · log₂(N₀/N). With carbon-14 (t½ ≈ 5730 years), 25% remaining gives an age of two half-lives ≈ 11,460 years.
Can I find the half-life itself?
Yes — given the initial and remaining amounts and the elapsed time, the tool solves t½ = t / log₂(N₀/N).
Does this work for non-radioactive decay?
Yes — any first-order (exponential) decay with a constant half-life follows the same equation, such as drug elimination described by a biological half-life.