Caffeine Calculator — Your Daily Caffeine Limit
Healthy adults are generally advised to keep caffeine under 400 mg per day, which is about four cups of brewed coffee. On a body-weight basis, 3 to 6 mg per kilogram is the usual range depending on your sensitivity — around 210 to 420 mg for a 70 kg adult. Caffeine has a half-life of about 5 hours, so a coffee at 4 PM still has a meaningful effect at 9 PM.
What is caffeine calculator?
Caffeine works by blocking adenosine, the compound that accumulates through the day and creates the sensation of sleepiness. It does not remove tiredness; it hides it.
Half-life is the practical number to remember. About five hours after a dose, half is still active in your system. That is why afternoon caffeine reliably damages sleep quality even for people who can fall asleep easily.
Content varies far more than people expect. A 240 ml brewed coffee averages 95 mg but ranges from 70 to 200 mg depending on bean, roast and brew method. Espresso has less per serving than drip coffee, not more.
How your caffeine limit is calculated
Your ceiling is your body weight multiplied by a sensitivity factor, capped at the widely cited 400 mg adult limit. The calculator then converts that into common drinks using typical caffeine contents. Bear in mind that real-world contents vary substantially between brands and preparation methods.
Daily limit (mg) = body weight (kg) × factor, capped at 400 mg
3 mg/kg sensitive · 5 mg/kg average · 6 mg/kg tolerant
Typical contents:
Brewed coffee 95 mg / 240 ml
Espresso 63 mg / shot
Black tea 47 mg / cup
Energy drink 80 mg / 250 mlSource: Based on the 400 mg/day adult guidance cited by the FDA and EFSA.
How to use this calculator
- Enter your body weight.
- Select how sensitive you are to caffeine.
- Read your daily limit in milligrams.
- Check the drink equivalents — this is where most people discover they are over.
- Stop caffeine at least 8 hours before bed to protect sleep quality.
Frequently asked questions
How much caffeine is safe per day?
Up to 400 mg per day is considered safe for most healthy adults. Pregnant people are generally advised to stay around 200 mg or less. Adolescents should consume considerably less.
Why can't I sleep after an afternoon coffee?
Caffeine's half-life is about five hours, so half of a 3 PM coffee is still active at 8 PM. Even if you fall asleep, it measurably reduces deep sleep. Stopping eight hours before bed is a good rule.
Does espresso have more caffeine than drip coffee?
Per serving, no. A single espresso shot has about 63 mg versus roughly 95 mg in 240 ml of drip coffee. Espresso tastes stronger because it is more concentrated, not because it contains more caffeine.
How much caffeine is in tea?
Black tea averages about 47 mg per cup, green tea around 30 mg, and white tea around 25 mg. Steeping time and water temperature change these figures considerably.
Is caffeine dependence real?
Yes. Regular use produces mild physical dependence, and stopping abruptly can cause headache, fatigue and irritability for two to nine days. These symptoms are temporary and not dangerous.
Related calculators
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- Water Intake Calculator — Calculate how much water to drink each day based on your body weight, exercise and climate. Results in litres, glasses and fluid ounces.
- Calorie Calculator — Free calorie calculator using the Mifflin-St Jeor equation. See how many calories you should eat to maintain, lose or gain weight, plus your BMR.
These figures are estimates from population formulas, not medical advice. Individual needs vary. If you are pregnant, managing a medical condition, or under 18, talk to a doctor before changing your diet.