Caffeine Calculator

Why track your caffeine

Caffeine turns up in coffee, tea, colas and energy drinks, and the FDA notes it can also be added to energy and protein bars, ice cream, chewing gum, dietary supplements and over-the-counter medicines. In moderate amounts it sharpens alertness, but too much can cause an increased heart rate, palpitations, high blood pressure, sleep disruption, anxiety, jitters, an upset stomach, nausea and headaches.

The catch is that few people know how much they actually take in. Content swings widely between products: the FDA lists 113–247 mg for a 12 fl oz cup of regular brewed coffee and 41–246 mg for the same volume of energy drink. People also differ, in the FDA’s words, “in both how sensitive people are to the effects of caffeine and how fast they eliminate it from the body.” The same two cups that one person barely notices can keep another awake at midnight. Adding up a typical day — and seeing how long it lingers — is the first step to finding an amount that suits you.

How to use this calculator

Enter how many of each drink you have on a typical day; half servings are fine. The sizes are standard servings, and an 8 fl oz cup is smaller than many mugs and most coffee-shop cups, so count a 16 fl oz mug of brewed coffee as two. For anything else — pre-workout powder, caffeine tablets, a specialty coffee or a brand that isn’t listed — type the total milligrams from the label into Pre-workout / other.

Add your body weight to see your intake per kilogram, and tick Pregnant or trying to conceive to compare your total against the lower 200 mg limit. If sleep is a concern, enter the hours from your last caffeine to bedtime for an estimate of what is still circulating when you turn in. A breakdown table under the results shows how much each drink contributes.

How it's calculated

Your total is each serving multiplied by its caffeine content, plus any milligrams you add yourself. The per-serving values come from USDA FoodData Central for coffee, tea and cola, and from manufacturers for energy drinks:

Your total is then compared with three benchmarks:

• 400 mg a day — the amount the FDA cites as not generally associated with negative effects for most healthy adults. The European Food Safety Authority (EFSA) uses the same figure, which it puts at about 5.7 mg per kg for a 70 kg adult.
• About 3 mg per kg in one sitting — EFSA’s level for single doses that raise no safety concerns, equal to 200 mg for a 70 kg adult. The calculator shows 3 mg × your weight in kg, capped at that 200 mg figure.
• 200 mg a day in pregnancy — ACOG’s committee opinion concluded that moderate intake below 200 mg a day does not appear to be a major contributing factor in miscarriage or preterm birth, and EFSA also uses 200 mg a day in pregnancy.

For bedtime, caffeine is assumed to leave your body exponentially with a 5-hour half-life, the mean reported by the Institute of Medicine, which also notes a range of about 1.5 to 9.5 hours: caffeine left = total × 0.5^{(hours ÷ 5)}. The low and high figures in the results apply the same formula with 1.5- and 9.5-hour half-lives.

Worked example

Jordan weighs 150 lb (68 kg). A typical day is two 8 fl oz cups of brewed coffee at 8 am, a can of cola with lunch at noon and an 8.4 fl oz energy drink at 4 pm, with bedtime at 11 pm.

• Total: (2 × 95) + 33 + 80 = 303 mg, or 76% of the 400 mg adult guide, so the calculator flags it as close to the limit.
• Per kilogram: 303 ÷ 68 = 4.5 mg/kg. Spread across the day that is within the daily guide, but drunk in one go it would exceed EFSA’s single-dose level of 200 mg.
• Bedtime: entering 7 hours treats all 303 mg as if taken at 4 pm, giving 115 mg (range 12–182 mg). That is deliberately an upper-end figure. Timing each drink separately — 24 mg left from the coffee, 7 mg from the cola and 30 mg from the energy drink — gives a more realistic 61 mg, but that is still enough that swapping the afternoon energy drink for a decaf option would help a light sleeper.
• If Jordan were pregnant, the same day would be 152% of the 200 mg limit.

Limitations & tips

Labels beat averages. Brand, bean, brewing method and serving size can easily double or halve the figures above, and coffee-shop drinks often come in 16–20 fl oz sizes. Where a label or company website lists milligrams, enter that number directly.

Half-life is personal. Smoking roughly doubles the rate at which caffeine is cleared, oral contraceptives can double its half-life, and pregnancy slows clearance further, to around 15 hours late in pregnancy. Liver disease and some medicines also prolong it, so treat the bedtime estimate as a guide rather than a measurement.

Beware concentrated caffeine. The FDA estimates that toxic effects such as seizures can occur with rapid consumption of around 1,200 mg of caffeine — less than half a teaspoon of the pure powder — which is why pure and highly concentrated caffeine products are so risky.

Cut back gradually. If you want to drink less, the FDA recommends reducing your intake gradually; withdrawal isn’t considered dangerous but can be unpleasant. This calculator is for healthy adults and is not medical advice. If you have a heart condition, high blood pressure or anxiety, take regular medication, or are pregnant or breastfeeding, ask your doctor what amount is right for you.

Sources & references

• U.S. Food and Drug Administration — Spilling the Beans: How Much Caffeine Is Too Much? — source of the 400 mg/day figure for healthy adults, symptoms of too much caffeine, typical ranges per 12 fl oz drink, the ~1,200 mg toxicity estimate and advice on cutting back.
• European Food Safety Authority — Caffeine — single doses up to 200 mg (about 3 mg/kg), 400 mg/day for adults, 200 mg/day in pregnancy, 3 mg/kg/day for children, and 100 mg near bedtime affecting sleep.
• American College of Obstetricians and Gynecologists — Committee Opinion 462: Moderate Caffeine Consumption During Pregnancy — source of the less-than-200 mg/day pregnancy guidance.
• Institute of Medicine — Caffeine for the Sustainment of Mental Task Performance: Pharmacology of Caffeine — mean half-life of about 5 hours, range 1.5–9.5 hours; oral contraceptives and smoking effects.
• StatPearls — Caffeine (NCBI Bookshelf) — half-life prolonged to up to 15 hours late in pregnancy and in liver disease.
• Temple et al. — The Safety of Ingested Caffeine: A Comprehensive Review (Frontiers in Psychiatry, 2017) — smoking doubles caffeine clearance; oral contraceptives double its half-life.
• USDA FoodData Central — caffeine per 100 g for brewed coffee (FDC 171890), espresso (171891), brewed black tea (173227), brewed green tea (171917) and cola (174852).
• Red Bull — How much caffeine is in a can of Red Bull Energy Drink? — 80 mg per 8.4 fl oz can and 151 mg per 16 fl oz can.