Math Calculators
Half-Life Calculator
Calculate remaining quantity after decay.
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About the Half-Life Calculator
Half-life is the time it takes for a quantity to fall to half its value — used for radioactive decay, drug metabolism, and more. Enter the initial quantity, the half-life, and the elapsed time (in the same units) and the calculator returns the amount remaining and the fraction left. It applies exponential decay: remaining = initial × 0.5^(time ÷ half-life).
How to use the Half-Life Calculator
- 01Enter your initial quantity, half-life, and elapsed time.
- 02Read the result instantly — it recalculates as you type.
- 03Adjust the numbers to model different scenarios.
Frequently asked questions
What is half-life?
The time for a quantity to decay to half its starting amount. After one half-life, 50% remains; after two, 25%, and so on.
How is remaining amount calculated?
Remaining = initial × (1/2)^(elapsed time ÷ half-life). Time and half-life must use the same units.