Caffeine: safe limits, half-life, and where it hides beyond coffee
For healthy adults, up to 400 mg of caffeine per day, and up to 200 mg in a single sitting, does not raise safety concerns. That is the conclusion of the European Food Safety Authority (EFSA), and it works out to roughly four to five espressos spread across a day. During pregnancy the advised ceiling halves to 200 mg per day. The catch most people miss is not the coffee they count but the caffeine they forget: tea, cola, energy drinks, chocolate and pre-workout powders all contribute to the same daily total, and caffeine's roughly 5 hour half-life means an afternoon dose is still working at midnight.
Up to 400 mg for healthy adults.
About 200 mg at once.
Roughly 5 hours on average.
What 400 mg looks like in real drinks
Caffeine content is not printed on most nutrition labels, so the milligrams below are typical values from EFSA's assessment; the linked Dietly pages show what the same drinks carry in sugar and calories, which is the other half of the story.
| Drink or food | Typical caffeine | Worth knowing |
|---|---|---|
| Single espresso (60 ml) | ~80 mg | Nearly calorie-free taken black |
| Filter coffee (200 ml) | ~90 mg | Mug size moves this a lot |
| Black tea (220 ml) | ~50 mg | Steeping time matters |
| Green tea drink | ~30 mg per cup brewed | Bottled versions add sugar, about 4 g per 100 ml on this label |
| Energy drink, 250 ml can | ~80 mg | 11 g sugar per 100 ml on this label, 27 g per can |
| Energy drink, 500 ml can | ~160 mg | Double volume doubles both caffeine and sugar |
| Cola (330 ml can) | ~40 mg | Zero versions keep the caffeine, drop the sugar |
| Dark chocolate, 50 g | ~25 mg | 450 kcal per 100 g on this label; the caffeine rides along |
| Pre-workout powder, 1 scoop | 150 to 300 mg | Check the tub; some scoops exceed the single-dose guideline alone |
A day with a morning filter coffee, an espresso after lunch, a can of energy drink and a few squares of chocolate sits near 275 mg, comfortably inside the guideline. Add a large pre-workout and the same day can clear 500 mg without a single drink feeling excessive.
The half-life math that ruins sleep
Caffeine's average elimination half-life is around 5 hours, with an individual range of roughly 2 to 8 hours depending on genetics, medications, smoking and pregnancy. Half-life math is unforgiving: a 200 mg coffee at 15:00 leaves about 100 mg circulating at 20:00 and about 50 mg at 01:00. Fifty milligrams is half an espresso, still enough to lengthen the time it takes to fall asleep and to shave deep sleep in sensitive people. If sleep is the problem, the evidence-based move is a caffeine curfew 8 or more hours before bed rather than quitting entirely. Slow metabolizers may need longer; fast metabolizers get away with more. You find your own line by moving the curfew, not by copying someone else's.
The company caffeine keeps
Caffeine itself is close to calorie-free, but its vehicles are not. The standard energy drink label above carries 11 g of sugar per 100 ml, which makes a 250 ml can worth about 27 g of sugar, more than half of the WHO's recommended daily free-sugar limit for a 2,000 kcal diet. Sugar-free versions such as Red Bull Zero and Monster Zero deliver the same caffeine at 2 to 3 kcal per 100 ml, and a bottled iced coffee lands in between with about 9 g of sugar per 100 ml. If you are managing both caffeine and calories, the sugar column of the label is where energy drinks differ; the caffeine content is surprisingly uniform. The comparison tool puts any two of them side by side.
Who should hold a lower line
- Pregnancy: EFSA advises no more than 200 mg per day across all sources.
- Adolescents: evidence is thinner; EFSA's single-dose guidance of about 3 mg per kg of body weight implies a much lower ceiling than the adult 400 mg.
- Anxiety and heart rhythm issues: caffeine can aggravate both; this is a talk-to-your-doctor zone, not a guideline zone.
- Poor sleepers: the half-life section above is the mechanism; the curfew is the fix.
Bottom line
Caffeine at everyday doses is one of the best-studied and safest stimulants we have: up to 400 mg per day for healthy adults, 200 mg at a time, 200 mg total in pregnancy. Count all sources, not just coffee, respect the 5 hour half-life when you schedule your last dose, and read the sugar line on caffeinated drinks, because that is where the labels genuinely differ.
Sources
Common questions
How much caffeine per day is safe?
The European Food Safety Authority concluded that up to 400 mg per day, and up to 200 mg in a single dose, does not raise safety concerns for healthy adults. During pregnancy the advised ceiling drops to 200 mg per day.
How long does caffeine stay in your system?
The average half-life is around 5 hours, with a wide individual range of roughly 2 to 8 hours. Half of a 200 mg afternoon coffee can still be circulating at bedtime, which is why late caffeine disturbs sleep.
Do energy drinks have more caffeine than coffee?
Usually not per serving. A standard 250 ml energy drink contains about 80 mg of caffeine, similar to a single espresso. Large cans and strong filter coffee both exceed that, so serving size decides.