About the Exponential Decay Calculator

The half-life model N(t) = N₀ × (1/2)^(t/T½) is the exponential decay law in its most intuitive form. With a half-life of 10 and 25 elapsed, the quantity has gone through 2.5 half-lives, leaving 100 × 0.5^2.5 ≈ 17.68 — under a fifth of the start.

Why "Half-Life" Is Constant

Decay probability per nucleus per unit time is fixed, so the fraction remaining after one half-life is always exactly 50%, regardless of how much is left. That constant ratio is what makes the curve an exponential — and why dating, dosing, and cooling all use the same mathematics.