Half-Life Decay Calculator
Enter the initial quantity, half-life and elapsed time to calculate how much remains.
Half-Life Decay Calculator
Calculate the remaining quantity of a substance after a given time, based on its half-life.
Half-life describes the time it takes for a quantity to reduce to half its value through exponential decay — used for radioactive isotopes, drug elimination in the body, and other decay processes. This calculator applies the standard exponential decay formula based on a substance’s half-life.
Example
- With the default values shown above, this calculator returns: Remaining Quantity ≈ 50.0000; Percent Remaining ≈ 50.00.
Frequently Asked Questions
What is the default example based on?
The default values use 5,730 years, the approximate half-life of carbon-14, a commonly cited example of radioactive decay used in radiocarbon dating.
Does this work for non-radioactive decay?
Yes — the same exponential decay formula applies to any process with a constant half-life, such as caffeine or medication elimination from the body, as long as you use the correct half-life for that process.