The Half-Life Calculator works with the time required for a quantity to decrease to half of its previous amount. Half-life is commonly used in radioactive decay, pharmacology, chemistry, and other exponential decay models.
Half-Life Formula
For repeated half-life decay, the remaining quantity can be written as N = Nβ(1/2)^(t Γ· tΒ½), where Nβ is the initial quantity, t is elapsed time, and tΒ½ is the half-life.
How to Use the Calculator
- Enter the known quantity or time values requested by the tool.
- Enter the half-life when it is known.
- Calculate the missing quantity or time.
- Check that all time units are consistent.
Example
If a substance has a half-life of 10 hours and starts with 80 units, after 10 hours 40 units remain. After 20 hours, 20 units remain, and after 30 hours, 10 units remain.
Important Point
Half-life describes a repeated proportional change, not a fixed amount removed during every interval. Each half-life leaves half of the amount present at the beginning of that interval. This is why the decay curve is exponential.