Caffeine Calculator
See How Long Caffeine Stays In Your System
Caffeine Metabolism Calculator
Model how your caffeine builds up and burns off across the day. Add your drinks, set your bedtime, and see how much is still in your system when your head hits the pillow.
1. Your Body
2. Your Drinks
Your Caffeine Curve
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Just for fun, not medical advice. This tool uses a simplified first-order elimination model and assumes caffeine is absorbed instantly. In reality caffeine peaks in the blood roughly 30 to 45 minutes after drinking, so early readings are approximate. Half-life varies widely (about 3 to 7 hours) based on genetics, medication, pregnancy, and liver health. Drink values are averages from USDA FoodData Central (generic drinks) and manufacturer labels (branded drinks). Consult a healthcare professional for personal guidance.
How Long Does Caffeine Stay In Your System?
Caffeine does not leave your body all at once. It fades in a predictable curve driven by its half-life, which is the time it takes for half the caffeine to clear. For most healthy adults that half-life sits between 3 and 7 hours, with about 5 hours being a common average. So if you drink a coffee with 96 mg of caffeine at 3 PM, roughly 48 mg is still active around 8 PM, and about 24 mg lingers near 1 AM.
What Is Caffeine Half-Life?
Half-life is the single biggest factor in how long a buzz lasts. A fast metabolizer clears caffeine in about 3 hours per cycle, while a slow metabolizer can take 8 hours or more. Pregnancy, certain medications, and liver function can push the half-life much longer. The calculator above lets you slide your own half-life to see how it reshapes the curve.
Does Body Weight Change Caffeine Effects?
Weight does not change how fast you clear caffeine, so your half-life and total milligrams stay the same. What weight does change is concentration, the intensity of the dose in your bloodstream. The same 128 mg double espresso is far more concentrated in a 120 lb person than a 250 lb person. This calculator estimates blood concentration using a standard volume of distribution of about 0.6 liters per kilogram, shown as your peak blood level in mg per liter.
How Much Caffeine Is Too Much?
The U.S. Food and Drug Administration points to 400 mg per day as an amount not generally associated with negative effects for healthy adults. That is roughly four 8-ounce cups of brewed coffee. The daily meter in the calculator tracks your total against that guideline. Pregnant people and those sensitive to caffeine should aim much lower.
Caffeine Content Of Common Drinks
Here are the average values this calculator uses. Espresso is especially variable, ranging from about 60 to 100 mg per shot depending on bean, roast, and extraction.
- Brewed coffee (8 oz): 96 mg
- Espresso, single shot: 64 mg
- Espresso, double shot: 128 mg
- Cold brew (8 oz): about 155 mg
- Black tea (8 oz): 47 mg
- Green tea (8 oz): 28 mg
- Matcha (1 tsp, 2 g): about 65 mg
- Diet Coke (12 oz): 46 mg
- Pepsi (12 oz): 38 mg
- Red Bull (8.4 oz): 80 mg
- Monster Energy (16 oz): 160 mg