Half-Life Calculator

About this calculator

This calculator applies the half-life decay formula — the amount remaining equals the starting amount times 0.5 raised to the power of (elapsed time divided by half-life) — to find how much of a substance is left after a given time, and what percentage has decayed. Half-life is the time it takes for exactly half of a quantity to decay, and because decay is exponential rather than linear, the amount never technically reaches zero, only gets closer and closer to it.

The concept is central to nuclear physics and radiometric dating, where the known half-life of an isotope (like carbon-14's roughly 5,730 years) lets scientists estimate the age of fossils and artifacts from how much of the isotope remains. It's equally important in medicine and pharmacology, where a drug's half-life in the body determines dosing intervals, and in nuclear medicine, where it determines how long a radioactive tracer or waste stays significantly radioactive.