Start with the caffeine amount on a label or in the drink amounts with links to their sourcesbase. This tool estimates the amount remaining after any number of hours; it doesn’t measure caffeine in your body.
Step 1
Enter a dose and elapsed time
Starting-dose shortcuts
Elapsed-time shortcuts
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 isn’t 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
Calculated caffeine remaining with a five-hour half-life
