Safe Daily Caffeine Intake Calculator — the 400 mg Line

How much caffeine is safe in a day depends on who is drinking it. The FDA puts the adult figure at 400 mg a day; pregnancy cuts that in half; and for children there is no safe target at all, only a ceiling. Pick your category below.

Where each number comes from

The three tiers do not share a single source, and it is worth knowing which agency stands behind each one.

Category	Daily figure	Who publishes it
Healthy adult	400 mg	FDA
Pregnant or breastfeeding	200 mg	ACOG, reported in StatPearls
Child or teen	3 mg per kg of body weight	EFSA (Europe) — no US per-kilogram number exists

The FDA’s wording is careful, and worth repeating: 400 mg is “an amount not generally associated with negative effects” for most adults, and the agency immediately notes there is wide variation in how sensitive people are and how fast they clear the drug. A 2017 systematic review by the Institute for the Advancement of Food and Nutrition Sciences reconfirmed that level.

Two to three 12-ounce cups of regular brewed coffee is the FDA’s own translation of 400 mg into cups. Our calculator uses a smaller reference cup — 8 fl oz, about 95 mg — so its cup count runs higher. Either way, cups are the least reliable unit in this whole subject; the caffeine content of common drinks varies by a factor of five between a green tea and a large energy drink.

The daily total is not a single-dose allowance

400 mg spread across a day and 400 mg swallowed at once are not the same event. EFSA separates the two explicitly: single doses up to 200 mg (about 3 mg per kilogram) raise no safety concern for a healthy adult, while the 400 mg figure applies only to intake “consumed throughout the day.” A concentrated pre-workout or a large energy drink can deliver the whole day’s allowance in ten minutes, which is where palpitations and tremor tend to show up.

EFSA also notes that a single dose as small as 100 mg can disturb sleep duration and pattern in some adults when taken close to bedtime — far below any safety ceiling. That is a timing problem rather than a dose problem, and it is governed by how long caffeine stays in your system.

Is 1,200 mg too much? Yes, and that is the real danger line

The FDA estimates that toxic effects, including seizures, can be observed with rapid consumption of around 1,200 mg of caffeine — less than half a teaspoon of the pure powder. Nobody reaches that on brewed coffee alone. It is a number attached to pure and highly concentrated caffeine products, bulk powders, and stacked energy drinks, which is exactly why the FDA has acted against that category.

Between 400 mg and 1,200 mg lies a wide band where most people simply feel awful rather than get hurt. The signs of too much caffeine page covers what that band feels like and how long it lasts.

When the ceiling does not apply to you

The published limits describe the general healthy population. StatPearls lists several situations that call for caution regardless of the number: documented arrhythmia, severe anxiety, peptic ulcer or reflux, liver or kidney impairment, and seizure disorders. Certain drugs matter too — caffeine competes for the CYP1A2 enzyme, which is why it interacts with some psychiatric medications and why ciprofloxacin can stretch its effects for hours.

For anyone under 18, the arithmetic is different again: see the caffeine limit for teens, where the American guidance is to avoid it rather than to dose it.

This content is informational and does not replace medical advice.