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About the Half-Life Calculator
This half-life calculator determines how much of a radioactive substance remains after a given time. Enter the starting quantity, the half-life, and the elapsed time, and the tool returns the remaining amount along with the number of half-lives that have passed.
The calculation relies on the standard decay formula N(t) = N₀ × (1/2)^(t/T), where N₀ is the initial quantity, t is the elapsed time, and T is the half-life. The exponent counts how many half-lives fit into the elapsed period, and each one cuts the remaining amount in half. The inputs are the starting amount, the half-life, and the time passed. A practical tip: keep the half-life and elapsed time in the same units, since mixing years with days is a common source of error.
- Enter the initial quantity of the substance.
- Input the half-life and the elapsed time in matching units.
- Read the remaining quantity from the result field.