Enter your body weight, select your caffeinated drinks (coffee, tea, energy drinks, cola, espresso), and specify quantities to calculate your total daily caffeine intake. The Caffeine Calculator compares your intake against the safe daily limit based on your weight and shows how much caffeine remains in your system at bedtime.
Total Caffeine Intake
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Your Safe Daily Limit
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Caffeine Remaining at Bedtime
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% of Safe Limit Used
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Safety Status
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For healthy adults, health authorities such as the FDA and EFSA recommend a maximum of 400 mg of caffeine per day. This is roughly equivalent to four 8-oz cups of brewed coffee. However, your personal safe limit may be lower depending on your body weight, sensitivity, medications, and health conditions.
A commonly used guideline is up to 5.7 mg of caffeine per kilogram (about 2.6 mg per pound) of body weight per day, with an absolute ceiling of 400 mg for most adults. For a single dose, no more than 200 mg at one time is generally recommended. This calculator uses your weight to estimate your personalized upper limit.
The biological half-life of caffeine in typical adults is 5 to 6 hours. This means if you consume 200 mg of caffeine at 8 AM, roughly 100 mg will still be in your system by 1–2 PM. Knowing this helps you understand how much caffeine remains in your body at bedtime, which can significantly affect sleep quality.
Yes, extremely high doses of caffeine can be fatal. The estimated lethal dose is approximately 150–200 mg per kilogram of body weight — for a 70 kg (154 lb) adult, that would be roughly 10,500 mg or more. While reaching this from beverages alone is very difficult, pure caffeine powder or supplements can pose a serious risk and have been linked to deaths.
Approximate caffeine content per serving: brewed coffee (8 oz) ~95 mg, espresso shot (1 oz) ~63 mg, instant coffee (8 oz) ~60 mg, black tea (8 oz) ~47 mg, energy drink (8.4 oz) ~80 mg, cola (12 oz can) ~34 mg. These are averages and actual amounts can vary significantly by brand and preparation.
Caffeine accumulates in your system. If you drink coffee at 7 AM and again at 10 AM, by 10 AM you still have around 70% of your first cup's caffeine circulating. The second dose adds on top, creating a higher combined peak than either cup would produce alone. This calculator accounts for this stacking effect based on your first caffeine time and bedtime.
Drinking coffee on an empty stomach can increase stomach acid production, potentially causing digestive discomfort or acid reflux in some people. It may also lead to a faster, more pronounced caffeine spike. While it isn't harmful for everyone, those with sensitive stomachs or acid reflux may benefit from having food alongside their caffeine.
Pregnant women are advised to limit caffeine to under 200 mg per day due to risks to fetal development. Adolescents and children should consume considerably less. People who are sensitive to caffeine, have anxiety disorders, heart conditions, high blood pressure, or take certain medications should also stay well below the 400 mg guideline and consult a healthcare professional.