Half-Life Calculator
Calculate remaining quantity after radioactive or exponential decay, or find the half-life from a decay measurement.
Result
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Half-lives elapsed —
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How it works
N(t) = N₀ × (1/2)^(t/half-life)Frequently Asked Questions
How do I calculate remaining amount after decay?
Multiply the starting amount by one-half raised to the number of half-lives elapsed: 100 g with a 5-year half-life leaves 50 g after 5 years, 25 g after 10 years, and about 12.5 g after 15 years.
How do I find a half-life from decay data?
Given a starting and current amount over a known time, the calculator solves half-life = t × ln(0.5) ÷ ln(N/N₀) — useful for carbon dating style problems or verifying a stated decay rate.
Does this apply to things other than radioactivity?
Yes — the same math describes drug elimination from the body, capacitor discharge, and any process where the rate of decrease is proportional to the current amount.