How much caffeine is OK
Two food safety agencies have published amounts for healthy people. The US Food and Drug Administration says that for most adults it has cited 400 mg a day as an amount not generally associated with negative effects. The European Food Safety Authority came to these conclusions in its 2015 opinion:
| Who | Amount EFSA found raises no safety concerns |
|---|---|
| Healthy adults, per day | Up to 400 mg |
| Healthy adults, single dose | Up to 200 mg (about 3 mg/kg) |
| Children and adolescents, per day | 3 mg per kg of body weight |
EFSA added that single doses of 100 mg may affect how long and how well some adults sleep, especially close to bedtime. The FDA points out that people vary widely in how sensitive they are to caffeine and how fast they clear it. These numbers are guidance for healthy people, not a target; if a doctor has told you to limit caffeine, follow that advice.
Caffeine in common drinks and foods
The calculator’s amounts come from USDA FoodData Central, which lists caffeine per 100 g; we multiplied it by the serving weight FoodData Central gives. The energy drink is EFSA’s example of a 250 ml can.
| Item | Serving | Caffeine | Source |
|---|---|---|---|
| Brewed coffee | 8 fl oz cup | 95 mg | FDC 171890 |
| Brewed coffee | 12 fl oz | 142 mg | FDC 171890 |
| Brewed coffee | 16 fl oz | 189 mg | FDC 171890 |
| Espresso | 1 fl oz shot | 63 mg | FDC 171891 |
| Decaf coffee | 8 fl oz cup | 2 mg | FDC 171889 |
| Black tea | 8 fl oz cup | 47 mg | FDC 173227 |
| Green tea | 1 cup | 29 mg | FDC 171917 |
| Cola | 12 fl oz can | 33 mg | FDC 174852 |
| Energy drink | 250 ml can | 80 mg | EFSA |
| Dark chocolate, 70 to 85% cacao | 1 oz | 23 mg | FDC 170273 |
| Milk chocolate | 1.55 oz bar | 9 mg | FDC 167587 |
Brands differ a lot. For a 12 fl oz serving, the FDA lists 23 to 83 mg for caffeinated soft drinks, 113 to 247 mg for regular brewed coffee and 41 to 246 mg for energy drinks. In the US, packaged foods with added caffeine must list it among the ingredients, while caffeine that comes naturally from an ingredient such as coffee, tea or chocolate is not listed on its own, and many products state the amount only voluntarily. When a label states the milligrams, use Other and enter that number.
Worked example
Say you drink an 8 fl oz cup of coffee at 8:00 and another at 13:00, then a can of cola at 16:00. That is 95 mg + 95 mg + 33 mg = 223 mg, or 56% of 400 mg. No single drink is above 200 mg.
Caffeine left at bedtime
Caffeine is broken down at a steady fraction per hour. Food Standards Australia New Zealand reports a half-life of 3 to 7 hours in adults, with first-order elimination at normal intakes, so after one half-life half of a dose is left, after two a quarter, and so on.
The calculator adds this up for every drink with a time, once with a 7-hour and once with a 3-hour half-life, and shows the range. In the example, with a bedtime of 22:30, about 21 mg to 77 mg would still be in your body. It treats each drink as absorbed at once, which FSANZ describes as rapid and complete, so the estimate is a little high for the hour after a drink.
How to use the caffeine intake calculator
- 1Choose who it is for. For a child of 2 or older or a teen, enter the body weight. For a child under 2 the calculator gives no amount, because the Dietary Guidelines for Americans say children under 2 should avoid drinks with caffeine.
- 2Tap Coffee, Espresso, Black tea or another button to add what you had, set the item, the number of servings and the time. Use Other for any product with the caffeine on its label.
- 3Read your total, how it compares with the guidance, and the estimate for bedtime. Use Copy result or Copy link to keep your day.
Staying hydrated is a separate question; the water intake calculator covers it. If late coffee keeps you up, the sleep cycle calculator helps you pick a bedtime.
Sources
- FDA: Spilling the beans: How much caffeine is too much? (400 mg a day for most adults, 12 fl oz ranges, caffeine on labels, children and teens)
- EFSA: Caffeine topic page, summary of the 2015 scientific opinion on the safety of caffeine (single dose, daily, children, sleep, energy drink example)
- USDA FoodData Central, SR Legacy: caffeine per 100 g and serving weights of the foods in the table
- Food Standards Australia New Zealand, P1056 Caffeine review, supporting document 1: safety assessment (2022), half-life (PDF)
Frequently asked questions
How much caffeine is too much in a day?
For most healthy adults, the FDA cites 400 mg a day as an amount not generally associated with negative effects. The European Food Safety Authority (EFSA) reached the same 400 mg a day for healthy adults. Both stress that people differ a lot in how sensitive they are to caffeine and how fast they clear it.
How much caffeine is in a cup of coffee?
USDA FoodData Central lists brewed coffee at 40 mg of caffeine per 100 g, about 95 mg in an 8 fl oz cup, and espresso at 212 mg per 100 g, about 63 mg in a 1 fl oz shot. Real drinks vary widely: the FDA gives 113 to 247 mg for a 12 fl oz cup of regular brewed coffee. If you know the amount of your drink, add it as Other.
How much caffeine can I have at once?
EFSA found that single doses of up to 200 mg, about 3 mg per kg of body weight, do not raise safety concerns for healthy adults. It also noted that 100 mg close to bedtime may affect sleep in some adults. The calculator flags any entry over 200 mg at one time.
How long does caffeine stay in your body?
Food Standards Australia New Zealand puts the half-life of caffeine in adults at 3 to 7 hours, meaning half of a dose is gone after that time. Add a time to each drink and a bedtime, and the calculator estimates how much is left when you go to sleep.
How much caffeine can children have?
EFSA proposed 3 mg per kg of body weight a day for children and adolescents, so a child of 30 kg would stay at or below 90 mg. The FDA notes that medical experts advise against energy drinks for children and teens, and that the Dietary Guidelines say children younger than 2 should avoid drinks with caffeine.