Dose + elapsed-time calculator
How much caffeine is left?
Start with the caffeine amount on a label or in the source-backed drink database. This tool estimates the amount remaining after any number of hours; it does not measure caffeine in your body.
Enter a dose and elapsed time
What the calculation means
CaffCalc applies remaining = dose × 0.5(elapsed hours ÷ half-life). With a five-hour half-life, the estimate halves every five hours: 200 mg becomes 100 mg after five hours, 50 mg after ten hours and 25 mg after fifteen hours.
A low calculated amount is not a promise that caffeine is gone or that sleep will be unaffected. Use the scenarios to compare timing decisions, not to diagnose sensitivity or choose a medically safe dose.
Common five-hour examples
| Starting dose | After 3 hr | After 6 hr | After 8 hr | After 10 hr | After 12 hr |
|---|---|---|---|---|---|
| 50 mg | 33 mg | 22 mg | 16 mg | 13 mg | 9.5 mg |
| 100 mg | 66 mg | 44 mg | 33 mg | 25 mg | 19 mg |
| 200 mg | 132 mg | 87 mg | 66 mg | 50 mg | 38 mg |
| 300 mg | 198 mg | 131 mg | 99 mg | 75 mg | 57 mg |
These values are generated directly from the published formula. See the worked guide for interpretation and sources.