Most healthy adults can safely consume up to 400 milligrams of caffeine per day, which works out to roughly two to three 12-ounce cups of brewed coffee. That’s the figure cited by the FDA and echoed by the European Food Safety Authority. But the right amount for you depends on your age, whether you’re pregnant, and how your body processes caffeine genetically.
The 400-Milligram Guideline
The 400 mg daily ceiling is the most widely referenced benchmark for healthy adults. The FDA describes it as “an amount not generally associated with negative effects,” and EFSA’s independent review landed on the same number. That said, this is a population-level guideline, not a personalized prescription. Some people feel wired after a single cup of coffee, while others drink four cups without noticing much.
EFSA also recommends keeping any single dose to 200 mg or less, roughly the amount in one strong cup of brewed coffee or a double espresso. Spacing your intake throughout the day matters because caffeine has a half-life of about five to six hours. If you drink a large coffee at 3 p.m., roughly half the caffeine is still circulating at 8 or 9 p.m., which is why afternoon cups can quietly wreck your sleep.
Limits During Pregnancy and Breastfeeding
The safe threshold drops to 200 mg per day if you’re pregnant or breastfeeding. The American College of Obstetricians and Gynecologists uses that figure for breastfeeding mothers, noting it “most likely will not affect your baby.” EFSA sets the same 200 mg limit for pregnancy based on fetal safety data. That’s roughly two 8-ounce cups of brewed coffee or four cups of black tea, with no room left over for a soda or chocolate bar without going over.
Guidelines for Children and Teens
The American Academy of Pediatrics recommends that children under 12 avoid caffeine entirely. For teens aged 12 to 18, the cap is 100 mg per day, about one 8-ounce coffee or two cans of cola. EFSA takes a slightly different approach, suggesting a body-weight-based limit of 3 mg per kilogram per day for children and adolescents. For a 90-pound (roughly 40 kg) teenager, that comes to about 120 mg.
Energy drinks are a particular concern for younger people. A single energy shot packs 113 to 200 mg of caffeine into just 2 to 2.5 ounces of liquid, and manufacturers aren’t required to declare the caffeine amount on the label. One shot could push a teen past their entire daily limit in seconds.
How Much Caffeine Is in Common Drinks
The numbers below are per 8-ounce serving, based on Mayo Clinic data:
- Brewed coffee: 96 mg
- Instant coffee: 62 mg
- Espresso (1 oz): 63 mg
- Black tea: 48 mg
- Green tea: 29 mg
- Cola: 33 mg
- Bottled black tea: 26 mg
- Decaf coffee: about 1 to 2 mg
Notice that an 8-ounce brewed coffee already contains 96 mg. Most mugs and café servings are 12 to 16 ounces, so a single “cup” from a coffee shop could easily contain 150 to 200 mg. If you’re tracking your intake, measure your actual serving size rather than assuming you drink neat 8-ounce portions.
Why Caffeine Hits Some People Harder
Your liver breaks down caffeine using a specific enzyme, and the gene that controls that enzyme (CYP1A2) comes in two main variants. People who carry two copies of the “fast” version clear caffeine efficiently. Those with one or two copies of the “slow” version keep caffeine circulating in their blood longer, which amplifies both the buzz and the side effects.
About 54% of the population are slow metabolizers. For these people, the same 400 mg that feels fine to a fast metabolizer can trigger anxiety, sleep disruption, and elevated blood pressure. Research has also linked slow-metabolizer status to a higher risk of heart problems as caffeine intake increases. If you’ve always felt that coffee “hits you harder” than it seems to hit other people, your genetics may genuinely process it differently, and a lower daily ceiling (closer to 200 mg) could be more appropriate for you.
Other factors slow caffeine metabolism too. Oral contraceptives can roughly double caffeine’s half-life, and pregnancy slows clearance significantly, which is one reason the recommended limit drops during those periods.
Signs You’re Getting Too Much
Your body gives fairly clear signals when you’ve crossed the line. Common symptoms of overconsumption include:
- Racing heart or palpitations
- Jitters or trembling hands
- Anxiety or irritability
- Insomnia or restless sleep
- Nausea or upset stomach
- Rapid, shallow breathing
- Headache
These symptoms can show up well below 400 mg in sensitive individuals. If you regularly experience any of them and you drink caffeine daily, try cutting your intake in half for a week and see if they improve. Caffeine withdrawal can cause headaches and fatigue for a few days, so tapering gradually is easier than quitting cold turkey.
Timing Matters as Much as Amount
Because caffeine’s half-life is five to six hours, when you drink it shapes how it affects you just as much as how much you drink. A 200 mg coffee at 7 a.m. will be mostly cleared by early afternoon. The same coffee at 2 p.m. leaves around 100 mg still active at bedtime. Even if you fall asleep fine, residual caffeine reduces the amount of deep sleep you get, which can leave you feeling groggy the next morning and reaching for more coffee, creating a cycle.
A practical rule: finish your last caffeinated drink at least 8 to 10 hours before you plan to sleep. For most people, that means a noon or early-afternoon cutoff. If you find yourself needing caffeine late in the day to function, that’s often a sign the caffeine itself is degrading your sleep quality overnight.