How much caffeine is in your blood right now?

The FDA considers up to 400 mg per day safe for most healthy adults, roughly four 8 oz cups of coffee or two 16 oz energy drinks. Pregnant or breastfeeding people should stay under 200 mg per day (ACOG), adolescents ages 12 to 17 under 100 mg (AAP), and children under 12 should avoid added caffeine. For reference, 200 mg (about one 12 oz brewed coffee or one Grande latte) is half the adult cap and the entire daily limit in pregnancy.

Research often cites a safe ceiling of about 3 to 6 mg of caffeine per kg of body weight per day. For a 70 kg (154 lb) adult that lands near 200 to 400 mg, in line with the FDA's 400 mg general limit. Lighter people and teens reach their limit sooner, so the same large coffee affects a 50 kg person far more than a 90 kg one. Enter your weight and the calculator scales your personal limit.

An 8 oz cup of brewed coffee has about 95 mg, a shot of espresso about 65 mg, a 12 oz cola about 35 mg, and an 8 oz black tea about 47 mg. Energy drinks vary widely: an 8.4 oz Red Bull is 80 mg and a 12 oz Celsius is 200 mg, while Bang, Reign, and Monster Java 300 push 300 mg in one can, close to the whole daily limit. Keep to one energy drink under 200 mg and avoid stacking it with coffee. Add any drink from the 82-drink database above to see your running total.

Per cup, no. A typical 8 oz matcha latte has about 70 mg of caffeine, while an 8 oz drip coffee has about 95 mg. Matcha pairs caffeine with L-theanine, which usually produces a steadier, less jittery feel even at lower doses.

Yes. A standard 8 oz decaf has about 2 to 7 mg, and a 16 oz decaf cafe drink can have 15 to 30 mg. Decaf is at least 97 percent caffeine-free under FDA labeling rules, not fully caffeine-free, so very sensitive people may still feel mild effects.

Caffeine has a half-life of 4 to 6 hours in healthy adults, so half of a 200 mg dose is gone in about 5 hours, half of the rest in another 5, and so on. Full clearance usually takes 20 to 30 hours. Pregnancy stretches the half-life to 9 to 15 hours, aging extends it modestly, and smoking shortens it.

Aim for at least 8 to 10 hours between your last meaningful caffeine dose and bedtime. Drake et al. 2013 (J Clin Sleep Med) found 400 mg taken 6 hours before bed still cut total sleep by about an hour. Even if you fall asleep on time, caffeine left in your system reduces deep slow-wave sleep, which is why a late coffee leaves you unrested. The calculator uses your personal half-life to show your exact cutoff time and estimated bedtime caffeine.

Yes, but ACOG recommends keeping intake under 200 mg per day, about one 12 oz brewed coffee or one Grande latte. The same cap applies while breastfeeding. Caffeine crosses the placenta freely and the fetus cannot metabolize it, and pregnancy also stretches your own caffeine half-life to 9 to 15 hours.

Mostly genetics. Variation in the CYP1A2 liver enzyme makes you a fast or slow metabolizer, and slow metabolizers feel effects roughly twice as long. Adenosine receptor density varies too, so the same 200 mg can feel like 100 mg for one person and 400 mg for another. This individual response is what caffeine sensitivity means, and the calculator lets you set your level so the bloodstream tracker scales correctly.

Yes, partial tolerance to the stimulant effects develops over 1 to 4 weeks of daily use. Tolerance to sleep disruption is much weaker, which is why long-time coffee drinkers can fall asleep after an evening cup but still get poorer sleep quality. The calculator does not discount for tolerance because the sleep impact persists.

Add each drink from the database and the calculator sums the total caffeine across all of them, then compares it to your personal daily limit. It also runs the half-life math on the combined dose, so the bloodstream tracker and sleep cutoff reflect everything you have had, not just your last cup. It is the easiest way to see whether your morning coffee plus an afternoon energy drink plus a soda pushes you past 400 mg.

Plain brewed coffee, espresso, and cold brew have zero sugar, but flavored drinks climb fast: a Grande Caramel Macchiato has 33 g, a Caffe Mocha 35 g, and a Caramel Frappuccino 54 g, the highest on the Starbucks menu. The American Heart Association caps added sugar at 25 g per day for women and 36 g for men, so a single sweet Grande can blow past it. Syrup, sweetener, and soda sugar all count as added sugar; the lactose in plain milk does not. The calculator tracks total drink sugar alongside caffeine.