Half-Life Decay Calculator
Chemistry & BiologyCalculate the remaining amount of a substance after radioactive or chemical decay over time.
Remaining Amount
The amount remaining after this elapsed time, based on exponential half-life decay.
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Chemistry & Biology calculators
Frequently Asked Questions
What is half-life?
Half-life is the time required for half of a given quantity of a substance to decay or be eliminated — a constant rate of proportional decay used to model radioactive isotopes, drug elimination, and other exponential decay processes.
Why must half-life and elapsed time use the same units?
The formula divides elapsed time by half-life to determine the number of half-life periods that have passed, so both values need consistent units, such as both in years or both in hours, for the calculation to be valid.
Does the substance ever reach exactly zero?
Mathematically, exponential decay only approaches zero asymptotically and never reaches it exactly, though after about ten half-lives the remaining amount becomes negligible for most practical purposes.
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