What this calculator does
Drug elimination by half-life works out fraction of a substance remaining or cleared after a given time, from its half-life. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaFraction remaining = 0.5^(elapsed time / half-life); about 97% is gone after 5 half-lives
The inputs explained
| Field | What to enter |
|---|---|
| Half-life (hours) | A number, measured in hours. Starts at 6. |
| Elapsed time (hours) | A number, measured in hours. Starts at 12. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with half-life
Every other input is held at the calculator’s starting values while half-life varies. Select any row to load that scenario into the calculator.