A familiar situation
Estimate the remaining amount in a decay exercise after several half-lives.
How to use this calculator
- Enter initial quantity, half-life duration, elapsed duration.
- Select Calculate to see the answer and its breakdown.
- Keep a scenario, change an input and compare the results.
Use consistent units and check the assumptions below before applying the result.
How half-life is calculated
Remaining amount = initial amount × (1/2)^(elapsed time / half-life). This continuous model works for any nonnegative elapsed duration; it does not predict individual decay events. After three half-lives, 80 mg becomes 80 × (1/2)³ = 10 mg.
Remaining quantity = initial×(1/2)^(elapsed/half-life).After three half-lives, 80 mg becomes 80 × (1/2)³ = 10 mg.
Assumptions & useful context
The result depends on the values you enter and the method described above. Displayed numbers may be rounded; calculations use the unrounded values. Check that this model matches your situation before relying on it.
Frequently asked questions
Does one half-life mean all material disappears?
No. It means the expected quantity is reduced by half.
Does the output account for environmental conditions?
No; it assumes the supplied half-life is constant and the system is not replenished.