For most healthy adults, the FDA says 400 milligrams of caffeine a day is not generally associated with negative effects. That is roughly two to three 12-ounce cups of coffee, depending on how strong the brew is. But that number is a ceiling, not a target.
The important catch is that caffeine tolerance varies a lot. Some people feel jittery, anxious, or unable to sleep at doses well below 400 mg. Energy shots, powders, and some supplements can also hide a lot more caffeine than people expect, which makes it easy to overshoot without noticing.
If caffeine gives you a fast heartbeat, shaky hands, stomach upset, or sleep problems, your personal limit is lower than the headline number. Pregnant people, teens, and anyone with heart rhythm concerns should be more cautious and use a clinician’s guidance instead of treating the FDA number as universal.
Sources
This is general information, not professional medical advice. For decisions about your situation, talk to a qualified professional.
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