Caffeine Calculator
How much caffeine is still in you through the day and at bedtime.
About this tool
Add each drink from the list (or a custom mg) with the time you had it, set your bedtime, and see a chart of caffeine remaining across the day using a five-hour half-life. The summary shows the day's total against the 400 mg guideline, the amount left at bedtime, and when it falls below 50 mg.
Half-lives, guidelines and sleep
Caffeine leaves the body exponentially: with a typical adult half-life of about five hours, half of a 95 mg coffee is still there at five hours and a quarter at ten, which is why a 4 pm coffee is a 25 mg dose at midnight. The 400 mg/day figure is what the European Food Safety Authority and the US FDA describe as not generally associated with adverse effects in healthy adults; guidance in pregnancy is 200 mg. Two honest caveats: caffeine content varies enormously by brew, bean and brand (the values here are typical, not measured โ a large coffee-shop filter can be 300 mg), and half-life ranges from 1.5 to 9.5 hours depending on genetics, oral contraceptives, pregnancy, smoking and some medicines, so the curve is an illustration of the principle rather than your blood level. General information, not medical advice. The sleep calculator works out bedtimes, the water intake calculator covers the other drink, and the timer runs a proper coffee brew.
Frequently asked questions
How long does caffeine stay in your system?
With a five-hour half-life, about 25% remains after ten hours and about 6% after twenty. Sensitive people notice effects at 30โ50 mg, hence the cut-off shown.
When should I stop drinking coffee before bed?
Research commonly cites six hours before bed for a standard cup; the chart lets you see what your own intake leaves at your bedtime.
Is 400 mg a safe limit?
It is the level health agencies cite for healthy adults; less if pregnant (200 mg), sensitive, or advised otherwise. Energy drinks and pre-workout reach it fast.
Are the drink values accurate?
They are typical published averages. Actual content varies by preparation โ check the can or ask the cafรฉ for precision.