Drug Half-Life Calculator

A half-life is the time it takes for half of what is present to be eliminated, and everything else follows from it by arithmetic. Enter the half-life and how long has passed to see the percentage left, the half-lives elapsed and the time to reach 90, 97 and 99 percent cleared. A second tab takes a dosing interval instead and works out the accumulation factor, the peak and trough at steady state and how long the build up takes. The half-life is an input because it belongs to the substance and to the person clearing it: age, liver and kidney function and other medicines all move it, and this page gives no advice on what to take or when.