Caffeine adds up quickly when it comes from a morning coffee, an afternoon tea, a soda at lunch and the occasional energy drink. This calculator totals what you have in a day from typical caffeine amounts, compares it with the guideline that fits you, and estimates how much is still in your system when you go to bed.
How to use the caffeine calculator
- Pick the guideline to compare with: a healthy adult (400 mg), pregnant (200 mg), breastfeeding (300 mg) or a teen (2.5 mg per kg of body weight).
- Enter how many of each drink or food you have on a typical day. Serving sizes are listed beside each item.
- Add any other caffeine from labels, such as pre-workout powder, caffeinated gum or pain relievers containing caffeine.
- Optionally enter your body weight (required for the teen guideline) and the hours between your last caffeine and bedtime.
Caffeine formulas
The bedtime estimate assumes a 5-hour half-life and that everything was consumed at once at your last drink, so it is an upper-end view of what is left; a 3–7 hour range is also shown.
Worked example
Two 8-ounce cups of brewed coffee and one 16-ounce energy drink, the last of them six hours before bed:
Coffee: 2 × 95 mg = 190 mg. Energy drink: 1 × 160 mg = 160 mg. Total = 350 mg.
That is 88% of the FDA's 400 mg level, leaving about 50 mg of room.
At bedtime: 350 × 0.56 ÷ 5 = 350 × 0.435 ≈ 152 mg still circulating, about as much as a large coffee.
Typical caffeine content
Approximate amounts, based largely on USDA FoodData Central; brands vary widely.
| Drink or food | Serving | Caffeine |
|---|---|---|
| Brewed coffee | 8 fl oz | about 95 mg |
| Espresso | 1 fl oz shot | about 63 mg |
| Cold brew coffee | 12 fl oz | about 155 mg (varies a lot) |
| Instant coffee | 8 fl oz | about 62 mg |
| Decaf coffee | 8 fl oz | about 2 mg |
| Black tea | 8 fl oz | about 47 mg |
| Green tea | 8 fl oz | about 28 mg |
| Cola | 12 fl oz | about 34 mg |
| Energy drink | 8.4 fl oz | about 80 mg |
| Energy drink | 16 fl oz | about 160 mg |
| Dark chocolate, 70–85% | 1 oz | about 23 mg |
| Caffeine tablet | 1 tablet | 200 mg |
Guidelines at a glance
| Who | Suggested daily limit | Source |
|---|---|---|
| Healthy adults | up to 400 mg | FDA |
| Pregnant or trying to conceive | under 200 mg | ACOG |
| Breastfeeding | up to about 300 mg | CDC |
| Teens | 2.5 mg per kg of body weight | Health Canada |
The FDA also warns that rapid intake of about 1,200 mg, the amount in roughly 0.15 tablespoon of pure powdered caffeine, can cause seizures. Highly concentrated caffeine powders and liquids are easy to overdose and best avoided.
Cutting back without the headache
Stopping suddenly can bring headaches, fatigue and irritability for a few days. Reduce by about one serving every few days, switch some cups to half-caff or tea, and keep the last caffeinated drink at least 6–8 hours before bed. If sleep is the concern, the sleep calculator helps set a bedtime, and the coffee ratio calculator lets you brew a slightly weaker pot on purpose.
Informational only — not medical advice. People with heart rhythm problems, anxiety disorders, high blood pressure or who take medications that interact with caffeine should ask a clinician about safe amounts.
Frequently asked questions
How much caffeine is too much?
The FDA says up to 400 milligrams a day is not generally associated with dangerous effects in healthy adults, about four or five cups of brewed coffee. Sensitivity varies widely, and some people get jittery or sleep badly on much less.
How much caffeine is safe during pregnancy?
The American College of Obstetricians and Gynecologists advises keeping caffeine below 200 mg a day during pregnancy. For breastfeeding, the CDC notes that up to about 300 mg a day is generally considered safe for the infant.
How long does caffeine stay in your system?
Caffeine's half-life in healthy adults is about 5 hours on average, with a range of roughly 3 to 7 hours. That means half of a 3 PM coffee can still be circulating at 8 PM. Pregnancy and some medications slow its clearance considerably.
Should teenagers have caffeine?
Pediatric groups discourage caffeine for children, and the American Academy of Pediatrics says energy drinks have no place in the diets of children and adolescents. Health Canada suggests teens limit caffeine to 2.5 mg per kilogram of body weight a day.
Why do caffeine numbers vary so much between sources?
Caffeine depends on the bean or leaf, roast, grind, brew time and serving size. A 16-ounce coffee-shop cold brew can contain twice as much as a home mug. Check labels on packaged drinks, which list caffeine in milligrams.