Find your personal daily limit, check today's intake, and see what time you need to stop drinking coffee for a good night's sleep.
The FDA's 400mg/day limit applies to a healthy 154lb adult. But your caffeine tolerance — and your safe upper limit — depends on your body weight, age, health conditions, and genetics. A 110lb teenager and a 220lb athlete have very different caffeine thresholds.
⏰ The sleep angle most people miss: Caffeine has a 5–6 hour half-life. A 200mg coffee at 3pm means ~100mg is still in your system at 8–9pm — enough to reduce sleep quality even if you fall asleep normally. This calculator shows your personal last-coffee cutoff time.
This calculator gives you your personalized daily limit, checks your current intake against it, and calculates how much caffeine will still be in your system at bedtime based on when you last consumed it.
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Caffeine Safety Calculator
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👤 About You
lbs
☕ Today's Caffeine Intake
🕐 Timing
⚕️ Note: Caffeine sensitivity varies significantly between individuals based on genetics (CYP1A2 enzyme variants), tolerance built from regular use, and medications. This calculator provides population-average estimates. If you experience palpitations, anxiety, or sleep disruption at doses below your calculated limit, reduce intake accordingly.
How Much Caffeine Is Too Much? 2026 Safety Guide
Caffeine is the world's most widely consumed psychoactive substance — and one of the most misunderstood in terms of safe dosing. The 400mg/day FDA guideline is widely quoted but rarely applied to individuals based on their actual weight and health status.
Beverage
Serving Size
Caffeine Content
Drip coffee
8 oz
80–200mg (avg 95mg)
Espresso
1 shot (1 oz)
60–75mg
Cold brew
8 oz
100–200mg
Red Bull
8.4 oz can
80mg
Monster
16 oz can
160mg
Bang / Celsius
16 oz can
300mg
Black tea
8 oz
40–70mg
Green tea
8 oz
25–45mg
Matcha latte
12 oz
60–80mg
Diet Coke
12 oz can
46mg
The Sleep Disruption Most People Don't Know About
Caffeine's half-life of 5–6 hours means a 3pm coffee still has significant active concentration at bedtime for most people. What most people don't realize is that caffeine doesn't just affect whether you fall asleep — it suppresses slow-wave sleep (deep sleep) even when you don't notice a difference in how quickly you fall asleep. Matthew Walker's sleep research consistently shows measurable deep sleep reduction from afternoon caffeine consumption even in people who report sleeping normally.
Genetic Variation in Caffeine Metabolism
The CYP1A2 enzyme is responsible for metabolizing approximately 95% of consumed caffeine. A genetic variant (CYP1A2*1F) makes some people "slow metabolizers" who retain caffeine 2–3 times longer than average. Slow metabolizers experience more pronounced anxiety, longer sleep disruption, and higher cardiovascular sensitivity per milligram consumed. At-home genetic tests (23andMe, AncestryDNA) can reveal your CYP1A2 status.
Frequently Asked Questions
How much caffeine is too much per day?
The FDA considers 400mg/day safe for healthy adults, but this is calibrated for a ~154lb person. Your personal limit scales with body weight: roughly 5.7mg per kg. A 110lb person's limit is closer to 280mg; a 200lb person can tolerate up to 520mg. Health conditions reduce safe limits significantly.
How long does caffeine stay in your system?
Caffeine has a 5–6 hour half-life in healthy adults. A 200mg dose at 2pm means ~100mg is still active at 7–8pm, ~50mg at midnight. Slow CYP1A2 metabolizers retain caffeine for 8–10+ hours. This explains why afternoon coffee disrupts sleep even when you feel alert.
What are symptoms of too much caffeine?
Mild overconsumption: jitteriness, anxiety, increased heart rate, headache, GI distress. Moderate: palpitations, tremors, insomnia, frequent urination. Severe (rare, requires very high doses): severe anxiety, vomiting, irregular heartbeat, seizures. If you experience palpitations after caffeine, reduce intake and consult a physician.
How much caffeine is safe during pregnancy?
Most guidelines recommend no more than 200mg/day during pregnancy — equivalent to about 2 cups of coffee. Some research suggests lower limits may be prudent. Caffeine crosses the placental barrier and fetal metabolism is significantly slower than adult metabolism. Consult your OB for personalized guidance.