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Half-Life Calculator
Solve one value in the half-life equation from the other three. See the remaining amount, percentage and elapsed half-lives without uploading data.
How do you calculate half-life and radioactive decay?
The model is remaining amount = initial amount × (1/2)^(elapsed time ÷ half-life). Choose which value to solve, enter the other three, and use the same time unit for elapsed time and half-life. After one half-life, 50% remains; after two, 25%. This is a mathematical model, not medical, safety or handling advice.
Frequently asked questions
How do you calculate half-life and radioactive decay?
The model is remaining amount = initial amount × (1/2)^(elapsed time ÷ half-life). Choose which value to solve, enter the other three, and use the same time unit for elapsed time and half-life. After one half-life, 50% remains; after two, 25%. This is a mathematical model, not medical, safety or handling advice.
Are my values uploaded?
No. This calculation runs locally in your browser. Values are not uploaded or saved.
How much remains after one half-life?
Half of the starting amount remains. After two half-lives, one quarter remains; after three, one eighth.
Can I solve for elapsed time?
Yes. Choose elapsed time, then enter the initial amount, remaining amount and half-life. Keep elapsed time and half-life in the same unit.
Can this calculator determine a safe dose or handling procedure?
No. It only evaluates an idealized exponential-decay equation. It does not calculate dose, exposure, shielding, contamination, medical risk or safe handling.