Half Life Calculator
Half-Life Calculator
Calculate drug half-life, elimination rate constant, or remaining drug amount.
Half-Life Formula
Where t½ is the half-life, k is the first-order elimination rate constant, D₀ is the initial amount, and D is the amount remaining after time t.
Drug Half-Life and Elimination
The half-life of a drug is the time required for its concentration or amount in the body to decrease by 50%. It is an important pharmacokinetic parameter used when determining dosing intervals, drug accumulation, and the time required to reach steady state.
For drugs exhibiting first-order elimination, the half-life is related to the elimination rate constant by the equation t½ = 0.693/k.
| Half-Lives Elapsed | Amount Remaining | Percentage Remaining |
|---|---|---|
| 0 | 1 × D₀ | 100% |
| 1 | 0.5 × D₀ | 50% |
| 2 | 0.25 × D₀ | 25% |
| 3 | 0.125 × D₀ | 12.5% |
| 4 | 0.0625 × D₀ | 6.25% |