Calculator tool
How this calculator works
Use the explanation to understand the formula, assumptions, and practical limits behind the calculator result.
What Half-Life Means
Half-life is the amount of time it takes for a quantity to fall to half of its current amount. After one half-life, 50% remains. After two half-lives, 25% remains. After three, 12.5% remains.
A Simple Example
Start with 80 grams of a substance that has a half-life of 10 days:
| Time | Amount left |
|---|---|
| 0 days | 80 g |
| 10 days | 40 g |
| 20 days | 20 g |
| 30 days | 10 g |
Where It Is Used
Half-life appears in radioactive decay, medicine, and any process where the same fraction disappears over equal time periods. It does not mean the substance suddenly vanishes after one half-life; it keeps shrinking by halves.
Read the Result Carefully
The formula works when the process follows steady exponential decay. If the decay rate changes over time, one half-life value is no longer enough to describe the whole process.
Frequently asked questions
How is the half-life concept applied to drug pharmacokinetics?
It is the time needed for the amount in the body to fall by half. After repeated half-lives, less remains, but the substance does not usually drop to zero all at once.
How does radiocarbon dating use half-life to determine artifact age?
Scientists compare how much radioactive material remains with how much was expected at the start. Because the material shrinks by a predictable fraction over time, the remaining amount helps estimate age.
What is the difference between physical, biological, and effective half-life?
Physical half-life describes radioactive decay itself. Biological half-life describes how fast the body removes a substance. In medicine, both ideas may matter.
Can the half-life of a radioactive element be changed?
For ordinary radioactive decay, the physical half-life is treated as a property of the isotope itself. Normal changes such as mixing or cooling do not make it decay faster or slower.
