Half-Life Simulator — Watch Radioactive Decay in Action

Drop 100 parent atoms in. Advance time one half-life at a time. The graph builds itself.

100 Atoms

Parent isotope Daughter isotope

In a real sample, each atom decays at a random moment — but with millions of atoms, the average always halves each half-life.

Data & Graph

Half-lives elapsed: 0
Parent remaining: 100 (100%)
Daughter formed: 0 (0%)
100% 50% 25% 0% 0 1 2 3 4 5 6 7 half-lives
% Parent % Daughter
HLParentDaughter%P

Notice: the % column halves each row (100 → 50 → 25 → 12.5 …). It never reaches zero.

Try it: estimate an age

A rock sample contains 12.5% of its original parent isotope. How many half-lives have passed? If the isotope is potassium-40 (HL = 1.25 billion years), what is the rock's age?

Use the simulator: advance until %P ≈ 12.5%. That gives you the number of half-lives directly. Multiply by 1.25 billion years.