Daily caffeine limit
How Much Caffeine Is Too Much Per Day?
Everyone has heard the number 400 mg. But what does that actually mean in coffee, tea, energy drinks, or soda? This guide covers the recommended daily caffeine limits, when they change, and why timing matters just as much as the total amount.
Where 400 mg comes from
400 mg is the ceiling for healthy adults, not a target. Roughly four to five cups of coffee. Past it, the evidence for side effects gets a lot stronger - jitteriness, elevated heart rate, disrupted sleep, anxiety. Under it, you're probably fine, but "probably" is doing real work in that sentence.
What counts toward your 400 mg
Coffee isn't the only source, and it isn't even the most concentrated one. Energy drinks and espresso pack more caffeine per ounce than a regular brewed cup. Soda and tea add up faster than people expect, especially across a full day.
When the limit changes
400 mg assumes a healthy, non-pregnant adult. Move outside that, and the number moves too.
- Pregnant: cap closer to 200 mg - higher intake is linked to lower birth weight.
- Under 18: no established safe limit. Most guidance says avoid it or stay well under 100 mg.
- On certain medications: some antibiotics and heart medications slow how fast caffeine clears, so the same dose sits active longer.
- Sensitive individuals: genetics alone can double how long caffeine stays active. Same 400 mg, different experience.
Why timing matters as much as the total
Caffeine has a half-life of roughly 5 hours. A coffee at 4 PM still has about half its caffeine active at 9 PM. Two cups spread across a morning clear very differently than two cups back to back at 3 PM. The total can stay under 400 mg and still wreck your sleep, because the total was never the whole story. OnBoard tracks this in real time instead of making you do the math - log a drink and watch the mg still active count down toward bedtime.
Signs you've gone over
The limit is a guideline. Your body gives you the real signal.
- Jitteriness or a racing heart within an hour of a drink
- Trouble falling asleep even hours after your last cup
- A wired, anxious feeling that doesn't match the moment
- A headache or fatigue when you skip caffeine - a sign of dependence, not just intake
Typical caffeine content by drink
| Drink | Serving | Caffeine |
|---|---|---|
| Energy drink | 240 ml can (8 oz) | ~80 mg |
| Brewed coffee | 240 ml (8 oz) | ~95 mg |
| Espresso | 30 ml shot (1 oz) | ~63 mg |
| Black tea | 240 ml (8 oz) | ~47 mg |
| Cola | 355 ml can (12 oz) | ~34 mg |
| Green tea | 240 ml (8 oz) | ~28 mg |
| Decaf coffee | 240 ml (8 oz) | ~3 mg |
Frequently asked questions
Is 400 mg the same for everyone?
No. It's the ceiling for healthy adults. Pregnancy, age, medications, and genetics all move it.
Does decaf count toward the limit?
Barely. A cup has a few milligrams - not zero, not enough to matter.
Can I "save up" caffeine for later in the day?
No. Caffeine clears on its own clock, roughly halving every 5 hours, regardless of when you drink it.
What happens if I go over 400 mg?
Jitteriness, elevated heart rate, and disrupted sleep all get a lot more likely. Not a hard cutoff, but risk climbs fast past it.
Does caffeine tolerance change the limit?
It changes how it feels, not how much is in your system. Tolerance masks the jitters - it doesn't speed up clearance.