Half-Life Calculator

Calculate remaining amount, elapsed time, or half-life for any exponential decay process.

Half-Life Calculator

N(t) = N₀ × (1/2)^(t / t₁/₂)
Example: Carbon-14 has a half-life of 5,730 years. Used in radiocarbon dating.

Remaining Quantity

250

out of 1,000

% Remaining

25%

Half-Lives Elapsed

2

Amount Decayed

750

Decay Constant (λ)

0.000121

N(11460) = 1000 × (0.5)^(2) = 250

Half-Life Calculator Formula & How It Works

N(t) = N₀ × (1/2)^(t/t½) = N₀ × e^(−λt)
  • N₀ = initial quantity
  • t½ = half-life (time for quantity to halve)
  • t = elapsed time
  • λ = decay constant = ln(2) / t½ ≈ 0.693 / t½

Half-life is the time required for half the substance to decay or transform. Used in nuclear physics, pharmacology (drug metabolism), and carbon-14 dating. After n half-lives, the fraction remaining is (1/2)ⁿ. After 1 half-life: 50%. After 5 half-lives: ~3.1%. After 10: ~0.1%. Carbon-14 has a half-life of 5,730 years.

Half-Life Calculator FAQs

What is the half-life of Carbon-14?

Carbon-14 has a half-life of 5,730 years. This makes it useful for dating organic materials up to ~50,000 years old. After 10 half-lives (57,300 years), only 0.1% remains — too little to measure accurately.

How is half-life used in pharmacology?

Drug half-life determines dosing intervals. After 4–5 half-lives, a drug reaches steady-state concentration. A drug with a 6-hour half-life reaches steady state after ~24–30 hours. Short half-life = need frequent dosing; long half-life = once-daily dosing.

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