Sleep cycles
Find optimal wake-up times or bedtimes based on 90-minute sleep cycles plus the time you need to fall asleep.
Open calculatorCaffeine remaining
Follows exponential decay: remaining caffeine = initial dose × 0.5^(hours elapsed / half-life). The average biological half-life of caffeine in healthy adults is roughly 5 hours (smoking shortens it, while pregnancy and oral contraceptives can lengthen it significantly).
mg
Caffeine remaining
100 mg
Percentage remaining
50%
The link may contain your inputs. Anyone receiving it can read them.
A 200 mg coffee with a 5-hour half-life still leaves roughly 100 mg active in your bloodstream 5 hours later.
Recent on this calculator
Full historyStored strictly in this browser’s local storage. Clicking an entry reloads the parameters into the calculator URL; sharing the link exposes those inputs to the recipient.
No saved calculations yet. Use any calculator and your recent results will appear here.
Educational estimate only. Not medical, tax, legal or financial advice.