Real-time, unit-aware calculator for radioactive (or exponential) decay. Type in any three fields — the rest update automatically.

💡 Tip: provide any three of {N(0), N(t), t, T/λ/τ}. The calculator solves the rest in real-time.

N(t) = N(0) · (1/2)^(t / T) = N(0) · e^(−λ·t) = N(0) · e^(−t/τ)
T = (ln 2) / λ        τ = 1/λ        T = τ · ln 2        ln 2 ≈ 0.693147