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Half-Life Calculator - Radioactive Decay

Free half-life calculator. Calculate remaining amount after radioactive decay. Works for any exponential decay process.

Calculate radioactive decay

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Half-Life Calculator

Calculate how much of a substance remains after radioactive decay. Also applies to drug metabolism, carbon dating, and other exponential decay.

N = N₀ × (1/2)^(t/t½)

N₀ = initial amount, t = time elapsed, t½ = half-life. After 1 half-life: 50% remains. After 2: 25%. After 3: 12.5%.

What are common half-lives?

Carbon-14: 5,730 years. Uranium-238: 4.5 billion years. Iodine-131: 8 days. Caffeine in body: 5 hours.

When is a substance 'gone'?

Never completely! But after 7 half-lives, <1% remains. After 10 half-lives, <0.1% remains.

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