There's a widely agreed number for healthy adults, and both US and European regulators land on it.
The 400 mg rule
Both the FDA and the European Food Safety Authority (EFSA) consider up to 400 mg of caffeine per day safe for most healthy, non-pregnant adults, roughly four cups of coffee.
What the maximum looks like in cups
The daily maximum is easier to respect once you know what each drink costs you:
- Drip coffee, 240 ml: about 95 mg, so roughly 4 cups
- Espresso shot: about 63 mg, so roughly 6 shots
- Instant coffee, 1 tsp: about 60 mg
- Energy drink, 250 ml: 80 mg and up, often far more per can
- Black tea: about 45 mg, so nearly 9 cups
There is also a limit per sitting
The daily number is not the only one. EFSA puts the safe single dose at about 200 mg, roughly two coffees at once. Spreading 400 mg across a day is a very different thing from drinking it in an hour, even when the daily total is identical.
Who should sit lower than 400 mg
- Pregnancy or breastfeeding: 200 mg
- Teenagers: roughly 2.5 mg per kg of body weight, so about 100 mg for a 40 kg teen
- Heart rhythm problems, anxiety disorders or bad insomnia: lower, and worth raising with your doctor
- Anyone on medication that slows caffeine clearance, including some antibiotics and oral contraceptives
Pregnancy is different
ACOG, EFSA and the NHS all recommend no more than 200 mg per day in pregnancy. Caffeine is cleared much more slowly then, and its half-life can rise to ~15 hours in the third trimester, so it accumulates.
Signs you are over your own limit
Your personal ceiling can sit well below 400 mg. The usual signals that you have passed it:
- Jitteriness, a racing heart, or anxiety
- Trouble falling or staying asleep
- Headaches, or an afternoon crash you “need” more caffeine to fix