Caffeine Intake: The 400 mg Guideline and How Much Is in Your Drinks
October 21, 2026
Caffeine is the world's most widely consumed stimulant. For most healthy adults, up to 400 milligrams a day, about four 8-ounce cups of brewed coffee, is not generally associated with adverse effects, according to guidance from the US Food and Drug Administration. People who are pregnant are usually advised to limit caffeine to 200 mg a day, and adolescents and people with certain conditions should limit intake further. Individual sensitivity varies widely because of genetics, body weight, medications, and habitual use.
The challenge is that the amount of caffeine in a drink varies greatly with the brand and the preparation. Knowing typical values helps you keep a running total.
Skip the math and get your answer instantly:
Open the Water Intake Calculator →Caffeine by Drink
The numbers below are typical values and ranges. Brewed coffee from specialty shops can run much higher than home-brewed coffee, and cold brew concentrates can be double or more.
| Drink | Serving | Caffeine (approx.) |
|---|---|---|
| Brewed coffee | 8 oz (240 mL) | 95 mg |
| Espresso | 1 oz shot | 63 mg |
| Black tea | 8 oz | 47 mg |
| Green tea | 8 oz | 28 mg |
| Cola | 12 oz can | 34 mg |
| Energy drink | 8 to 16 oz | 80 to 300 mg |
| Dark chocolate (70%) | 1 oz | 23 mg |
| Decaf coffee | 8 oz | 2 to 5 mg |
Totaling Your Day
A typical day might include a 12-ounce coffee (about 140 mg), an afternoon tea (47 mg), and a cola with lunch (34 mg), totalling about 221 mg. Adding a large 20-ounce coffee (about 240 mg) and a pre-workout supplement with 200 mg quickly pushes you beyond 400 mg.
To find your total, list every source, including medications and supplements that contain caffeine. Check labels for pre-workout powders, pain relievers, and weight-loss products, which can include substantial doses.
Timing and Sleep
Caffeine has a half-life of about five hours in most adults, though it ranges from 2 to 10 hours depending on genetics, liver function, smoking, and medications. That means a 200 mg coffee at 3 p.m. leaves about 100 mg in your system at 8 p.m. and 50 mg at 1 a.m. Studies find that caffeine taken even six hours before bedtime can reduce total sleep time.
A common recommendation is to stop caffeine at least 8 hours before bed. If you have trouble sleeping, move your last cup earlier and watch hidden sources like tea, chocolate, and soda.
Side Effects and Warning Signs
Too much caffeine can cause jitteriness, anxiety, a fast heartbeat, upset stomach, headaches, and trouble sleeping. Regular heavy users who stop suddenly may experience withdrawal headaches, fatigue, and irritability for several days. Very high single doses, such as from pure caffeine powder, can be dangerous or fatal, and a teaspoon of powder can contain the equivalent of dozens of cups of coffee.
People with anxiety disorders, heart rhythm problems, high blood pressure, or reflux, and those who take certain medications, should discuss caffeine limits with a clinician.
Cutting Back Gradually
Reduce by about 25% every few days, mixing decaf into your regular coffee, or swapping one cup for tea. Drink water alongside, get enough sleep, and expect a week or so of adjustment. Caffeine does not replace sleep, so address the underlying cause of fatigue.
Frequently Asked Questions
How much caffeine is safe per day?
Up to 400 mg for most healthy adults, according to FDA guidance. Pregnant people are advised to limit to 200 mg.
How much caffeine is in a cup of coffee?
About 95 mg for an 8-ounce cup of brewed coffee, though it varies widely.
Does caffeine dehydrate you?
In regular consumers, the mild diuretic effect is offset by the fluid in the drink, so caffeinated beverages still contribute to hydration.
How long does caffeine stay in your body?
Its half-life averages about five hours, so effects can last well into the evening.
Is caffeine addictive?
It causes physical dependence in regular users, with withdrawal symptoms when stopped, but it differs from addiction to substances that cause severe harm.