Caffeine Calculator,
know your daily limit.

Field guide

Caffeine, the FDA limit, and why it matters.

Caffeine is the world's most widely consumed psychoactive substance. It works by blocking adenosine receptors in the brain, the receptors that promote sleepiness, which is why a cup of coffee makes you feel alert. In moderate amounts it is safe for most healthy adults. In large amounts it can cause restlessness, anxiety, rapid heartbeat, headaches, and in extreme cases, serious cardiac events.

The FDA recommended limit

For healthy adults, the US Food and Drug Administration (FDA) recommends a maximum of 400 milligrams of caffeine per day. That is roughly the amount in four standard cups of drip coffee. Above that threshold, the risk of adverse effects rises noticeably for most people, though individual tolerance varies widely based on genetics, body weight, medications, and habitual consumption.

The European Food Safety Authority (EFSA) reaches a similar conclusion: 400 mg per day for adults, and up to 200 mg in a single dose, are levels that do not raise safety concerns for the general healthy adult population.

How much caffeine is in common drinks?

Caffeine content varies by drink type, preparation method, and brand. The values this calculator uses are midpoints from published FDA and Mayo Clinic data:

• Drip coffee (8 oz): about 95 mg. Filter brewing extracts a moderate amount of caffeine; a lighter roast often has slightly more than a dark roast because roasting partially degrades caffeine.
• Espresso (1 oz shot): about 63 mg. A single shot is much more concentrated than drip coffee, but the serving size is smaller. A double espresso or a milk-based drink made with two shots contains around 126 mg.
• Black tea (8 oz): about 47 mg. Brew time and water temperature affect extraction significantly. Loose leaf brewed for 5 minutes can reach 90 mg.
• Green tea (8 oz): about 28 mg. Lower than black tea due to less oxidation during processing, though matcha (concentrated powdered green tea) can contain 70 mg or more per serving.
• Energy drink (8 oz can): about 80 mg per standard 8 oz can. Larger cans (16 oz, 24 oz) are common and contain proportionally more. Always check the label, since caffeine content varies widely by brand.
• Cola or soda (12 oz): about 34 mg for classic cola. Citrus sodas are typically caffeine-free. Pepsi Max and some other diet sodas contain more, around 70 mg per 12 oz.

What happens when you go over 400 mg?

Exceeding 400 mg does not guarantee harm, especially for those with a high habitual tolerance, but the risk of side effects rises. Common signs of too much caffeine include:

• Jitteriness, restlessness, and difficulty concentrating
• Increased heart rate or palpitations
• Headache or dizziness
• Gastrointestinal discomfort or acid reflux
• Difficulty falling or staying asleep
• Elevated blood pressure (relevant for those with hypertension)

Very high doses, typically above 1,200 mg taken rapidly, can cause toxic effects. Deaths have been reported from concentrated caffeine powder or pill products, not from beverages, but the risk illustrates why the 400 mg guideline exists.

Who should consume less than 400 mg?

The 400 mg guideline applies to healthy, non-pregnant adults. Several groups should consume significantly less:

• Pregnant women: Both the FDA and EFSA recommend limiting intake to 200 mg per day. Higher amounts have been linked to low birth weight and pregnancy loss in some studies, though the research is not fully settled.
• Children and adolescents: There is no established safe level for children. Paediatric guidelines generally advise avoiding caffeine entirely in young children and limiting it to about 85 to 100 mg per day in teenagers.
• People with anxiety disorders: Caffeine can worsen generalised anxiety, panic attacks, and sleep disorders.
• Those with heart conditions: Arrhythmias and some structural heart conditions can be aggravated by caffeine. Individual responses vary; follow your doctor's guidance.
• People on certain medications: Caffeine interacts with some antibiotics (ciprofloxacin, norfloxacin), bronchodilators (theophylline), lithium, and clozapine. Always check with a pharmacist if you are on regular medication.

Caffeine timing and sleep

Caffeine has a half-life of about five to six hours in most adults. That means if you drink 200 mg at 3 pm, roughly 100 mg is still active in your system at 8 or 9 pm. For better sleep quality, most sleep researchers suggest cutting off caffeine by early afternoon, around 12 to 2 pm for people who want to be in bed by 10 or 11 pm.

Caffeine sensitivity to sleep disruption is partly genetic. Some people metabolise caffeine quickly (fast metabolisers) and can drink an espresso after dinner with no sleep impact. Slow metabolisers feel caffeine effects for much longer, and even a morning cup can subtly worsen sleep quality that night.

Reducing caffeine intake gradually

Stopping caffeine abruptly after regular high consumption can cause withdrawal symptoms: headache, fatigue, irritability, and difficulty concentrating, usually starting 12 to 24 hours after the last dose and peaking at 20 to 51 hours. These symptoms are temporary and typically resolve within two to nine days.

A gradual taper is the most comfortable approach. Reduce your daily intake by about 10% every few days, switching progressively to lower-caffeine alternatives (half-caf coffee, black tea, green tea) until you reach your target level.

Disclaimer

This calculator uses average caffeine values from published sources. Actual caffeine content in your specific drink may differ based on brand, brewing method, and serving size. The 400 mg limit applies to healthy, non-pregnant adults. This tool is for informational purposes only and is not a substitute for medical advice.