Radioactive Decay and Half-Life Calculator
Works through half-life problems. Choose what to find; the field for that value is ignored.
Answer
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Amount remaining —
Percent remaining — %
Half-lives elapsed —
Decay constant — per second
Reading this —
The formula
N = N₀ × (½)^(t ÷ t½) λ = ln 2 ÷ t½
After each half-life, half of what was left remains.
What to watch out for
The default half-life is carbon-14, at about 5,730 years.
Frequently Asked Questions
How much of 100 g is left after two half-lives?
25 g: half, then half again.
How long until 10% of a sample with a half-life of 5,730 years remains?
About 19,035 years, which is 3.32 half-lives.