How much caffeine is safe per day?

The FDA recommends that healthy adults consume no more than 400 mg of caffeine per day — roughly 4 cups of brewed coffee. Pregnant or breastfeeding women should limit intake to 200 mg, and adolescents to 100 mg. Children under 12 should avoid caffeine entirely.

What is the half-life of caffeine?

Caffeine has an average half-life of about 5 hours in healthy adults, meaning half of the caffeine you consume is still in your body 5 hours later. Half-life varies from 3 to 7 hours based on genetics, pregnancy, smoking, and medications.

How long before bed should I stop drinking caffeine?

Because caffeine has a 5-hour half-life, you should stop consuming it at least 8 hours before bedtime. For most people, that means no coffee or energy drinks after 2 PM if you go to bed at 10 PM.

How much caffeine is in a cup of coffee?

An 8 oz cup of brewed coffee contains about 95 mg of caffeine. A single espresso shot has about 63 mg, and an instant coffee has about 62 mg. Decaf still contains about 2 mg per cup.

How much caffeine is in an energy drink?

An 8.4 oz Red Bull has about 80 mg of caffeine. A 16 oz Monster or Rockstar has about 160 mg. High-performance energy drinks like Bang can contain up to 300 mg per 16 oz can.

Can caffeine affect sleep?

Yes. Caffeine blocks adenosine receptors in the brain, which delays the onset of sleep and reduces deep sleep quality. To protect sleep, keep caffeine below 50 mg in the 8 hours before bedtime.

About Caffeine Math

Free, independent caffeine tools built by coffee drinkers, for coffee drinkers. No signup, no ads, no tracking.

Why we built this

Caffeine is the most widely consumed psychoactive substance in the world — about 80% of US adults drink it every day. Yet most of us have no idea how much we're actually consuming. A "cup of coffee" can mean anything from 95 mg (generic 8 oz drip) to 310 mg (a Starbucks Grande Pike Place), and a 16 oz energy drink can pack as much caffeine as three cups of coffee in a single can.

We built Caffeine Math because we needed it ourselves. One of us was a competitive cyclist who wanted to time pre-workout caffeine for performance without ruining sleep. Another was pregnant and trying to stay under the 200 mg/day limit recommended by ACOG. A third was just tired of being tired at 3 PM and not understanding why their morning coffee had stopped working.

Every existing tool we tried was either a single-function calculator, a calorie tracker that buried caffeine three taps deep, or an ad-stuffed content farm that wouldn't let you actually use the tool without scrolling past four pop-ups. So we built the tool we wanted: fast, free, no signup, with the actual caffeine data on the same page as the calculator.

What we offer

Caffeine Math is a suite of free tools covering the entire caffeine lifecycle — from understanding what's in your cup, to planning when to stop drinking it, to managing withdrawal when you quit. Our tools include:

Caffeine Intake Calculator — add everything you drank today and see if you're within the safe daily limit for your demographic.
Caffeine Half-Life Calculator — find out when your last cup will drop below the sleep-safe threshold of 50 mg.
Caffeine Content Database — search 40+ beverages and foods for exact caffeine content per serving.
Drink Comparison Tool — compare up to 5 beverages side-by-side to see which packs the most caffeine.
Body-Weight Safe Limit Calculator — see your personalized caffeine ceiling based on body weight (3–6 mg/kg), capped at the FDA's 400 mg/day limit.
Coffee Brewing Ratio Calculator — find your brew strength and estimate caffeine extraction based on coffee grams, water, and bean type.
Caffeine Withdrawal Timeline — see where you are in the 2–9 day withdrawal process and when symptoms will resolve.

Our data sources

Every caffeine value on this site comes from one of these sources, cited per page where relevant:

USDA FoodData Central — the U.S. Department of Agriculture's nutrient database, the standard reference for caffeine content in foods and beverages.
FDA — the U.S. Food and Drug Administration's published guidance on safe caffeine intake (400 mg/day for healthy adults).
EFSA — the European Food Safety Authority's scientific opinion on caffeine safety (400 mg/day single dose, 200 mg for pregnant women).
ACOG — the American College of Obstetricians and Gynecologists' Committee Opinion on moderate caffeine consumption during pregnancy (≤200 mg/day).
AAP — the American Academy of Pediatrics' guidance on caffeine for children and adolescents (avoid under 12, ≤100 mg for 12–18).
Peer-reviewed research — cited per page in the long-form guides, with links where available.
Manufacturer labels — for branded products (Starbucks, Red Bull, Monster, Bang), we use the caffeine values published by the manufacturer on the product label or website.

Who we are

Caffeine Math is built and maintained by a small team of developers, designers, and health-curious coffee drinkers. We have no medical advisors on staff, which is why every page includes a medical disclaimer pointing you to a healthcare professional for personalized guidance. We're a tool, not a doctor.

The site is funded entirely out of pocket. We have no investors, no advertisers, and no affiliate relationships with any beverage brand or supplement company. We don't sell anything, and we never will. If we ever change that policy, we'll update this page first.

Our editorial policy

All caffeine values are updated when source data changes. When a beverage brand reformulates (e.g., Bang reducing caffeine from 300 mg to 250 mg), we update the database within 30 days. When new research shifts the consensus on safe limits (e.g., the 200 mg pregnancy limit, which has been debated), we update the relevant guide page and add a note explaining the change.

We do not accept guest posts, sponsored content, or paid placements. All guides are written by us and fact-checked against the cited sources before publication. If you spot an error, please contact us and we'll fix it within 7 days.

Contact & feedback

Found a bug? Have a feature request? Spotted outdated caffeine data? We'd love to hear from you. Visit our contact page to send feedback, suggest a new tool, or request a correction.

Mission

Help coffee drinkers understand exactly how much caffeine they consume, stay under safe limits, and protect their sleep — for free, with no signup or tracking.

Sources

Caffeine values are drawn from USDA FoodData Central, FDA published guidance, EFSA, the American College of Obstetricians and Gynecologists, and peer-reviewed research cited per page.

Independence

We are not affiliated with any beverage brand. We don't sell supplements, accept sponsored placements, or run ads. The tools exist because we needed them ourselves.

Last updated: October 2026. This page is reviewed quarterly and updated whenever our data sources or policies change.