Half-Life Calculator
Calculate remaining quantity, elapsed time, or half-life of any decaying substance.
The Half-Life Formula
Half-life is the time for half a quantity to decay: N(t) = N₀ × (1/2)^(t/T), where N₀ is initial amount, T is half-life, t is elapsed time. Decay constant λ = ln(2)/T. Used in nuclear physics, archaeology (carbon dating), and pharmacology.
Decay Inputs
Initial Quantity (N₀)
Half-Life (T)
Elapsed Time (t)
Result
Remaining (N)
125
Decayed
875
Fraction Remaining
12.5%
Half-Lives Elapsed
3
Decay Constant (λ)
0.1386
Mean Lifetime (τ)
7.21
N = 1000 × (1/2)^(15/5) = 1000 × 0.125 = 125