What this calculator does
Caffeine remaining in the body works out estimates caffeine left in your system over time using first-order elimination kinetics. 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
The inputs explained
| Field | What to enter |
|---|---|
| Caffeine consumed (mg) | A number, measured in mg. Starts at 200. |
| Assumed half-life (hours) | A number, measured in hours. Starts at 5. |
| Time since consumption (hours) | A number, measured in hours. Starts at 6. |
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 caffeine consumed
Every other input is held at the calculator’s starting values while caffeine consumed varies. Select any row to load that scenario into the calculator.
| Caffeine consumed (mg) | Caffeine remaining | Share of dose remaining | Note |
|---|---|---|---|
| 100 | 44 mg | 43.5% | Average adult half-life is roughly 5 hours, but it ranges widely (about 1.5-9.5 hours) with genetics, pregnancy, liver function and other drugs. |
| 150 | 65 mg | 43.5% | Average adult half-life is roughly 5 hours, but it ranges widely (about 1.5-9.5 hours) with genetics, pregnancy, liver function and other drugs. |
| 200 | 87 mg | 43.5% | Average adult half-life is roughly 5 hours, but it ranges widely (about 1.5-9.5 hours) with genetics, pregnancy, liver function and other drugs. |
| 300 | 131 mg | 43.5% | Average adult half-life is roughly 5 hours, but it ranges widely (about 1.5-9.5 hours) with genetics, pregnancy, liver function and other drugs. |
| 400 | 174 mg | 43.5% | Average adult half-life is roughly 5 hours, but it ranges widely (about 1.5-9.5 hours) with genetics, pregnancy, liver function and other drugs. |
| 600 | 261 mg | 43.5% | Average adult half-life is roughly 5 hours, but it ranges widely (about 1.5-9.5 hours) with genetics, pregnancy, liver function and other drugs. |