About

Caffeine follows first-order elimination kinetics with a plasma half-life (t_½) averaging 5 hours in healthy adults. Genetic polymorphisms in CYP1A2 shift this range from 1.5 to 9.5 hours. The FDA caps daily intake at 400 mg for adults. Exceeding this threshold correlates with anxiety, tachycardia, and sleep-onset latency increases. Miscounting caffeine is common because sources vary: a 30 mL espresso shot contains roughly 63 mg, while a 355 mL energy drink can exceed 160 mg.

This calculator aggregates your consumed sources, computes total intake against the FDA ceiling, models blood concentration decay over time, and estimates the hour your system drops below the 50 mg sleep-disruption threshold. It approximates clearance assuming hepatic metabolism under normal conditions. Pregnancy, liver disease, and concurrent medications (fluvoxamine, oral contraceptives) can double or triple t_½. Adjust the sensitivity setting accordingly.

Formulas

Blood caffeine concentration at time t follows first-order exponential decay:

C(t) = C₀ × 0.5^tt_½

Where C₀ = initial caffeine dose (mg), t = elapsed time (hours), and t_½ = elimination half-life (default 5 h).

To estimate clearance time to a target threshold C_target:

t_clear = t_½ × log₂(C₀C_target)

Where C_target = 50 mg (threshold below which caffeine minimally disrupts sleep onset).

FDA daily limit for healthy adults: 400 mg. Risk dose: 10 mg/kg body weight. Percentage of limit:

P = Total Intake400 × 100%

Reference Data

Beverage / Source	Serving Size	Caffeine (mg)	Notes
Espresso (single shot)	30 mL	63	Varies by roast and machine pressure
Drip Coffee (brewed)	240 mL	96	Light roasts slightly higher than dark
Cold Brew Coffee	240 mL	200	Concentrate; dilution varies
Instant Coffee	240 mL	62	Freeze-dried granules
Decaf Coffee	240 mL	5	Not zero; residual caffeine remains
Black Tea	240 mL	47	Steep time affects extraction
Green Tea	240 mL	28	Contains L-theanine (modulates effect)
White Tea	240 mL	15	Lowest among true teas
Matcha	240 mL	70	Whole-leaf powder; higher per gram
Yerba Mate	240 mL	85	Traditional gourd serving
Chai Latte	240 mL	50	Black tea base with spices
Coca-Cola (Classic)	355 mL	34	Standard can
Diet Coke	355 mL	46	Higher than regular Coca-Cola
Pepsi	355 mL	38	Standard can
Mountain Dew	355 mL	54	Citrus soda
Red Bull	250 mL	80	Standard can; also contains taurine
Monster Energy	473 mL	160	Full can (16 oz)
Bang Energy	473 mL	300	High-caffeine energy drink
5-hour Energy (shot)	57 mL	200	Concentrated liquid shot
Dark Chocolate (70-85%)	28 g	23	Per 1 oz square
Milk Chocolate	28 g	6	Per 1 oz square
Hot Chocolate	240 mL	5	Cocoa-based preparation
Caffeine Pill (NoDoz)	1 tablet	200	Pharmaceutical-grade anhydrous caffeine
Pre-Workout Supplement	1 scoop	250	Varies by brand; check label
Excedrin (Extra Strength)	1 tablet	65	Acetaminophen + aspirin + caffeine
Midol Complete	1 caplet	60	Menstrual relief with caffeine
Iced Tea (commercial)	355 mL	25	Bottled/canned sweetened
Kombucha	240 mL	15	Fermented tea; varies widely
Coffee Ice Cream	132 g	30	Per ½ cup serving
Turkish Coffee	60 mL	50	Unfiltered; fine grind boiled

Frequently Asked Questions

The CYP1A2 enzyme metabolizes ~95% of ingested caffeine. "Fast metabolizers" (CYP1A2*1A homozygotes) clear caffeine with a half-life near 3 hours. "Slow metabolizers" (CYP1A2*1F carriers) can have half-lives exceeding 9 hours. Smoking induces CYP1A2, reducing half-life to ~3 hours. Oral contraceptives inhibit it, roughly doubling half-life to ~10 hours. Use the sensitivity slider to approximate your phenotype.

Research published in the Journal of Clinical Sleep Medicine (2013) found that 400 mg caffeine taken 6 hours before bed significantly disrupted sleep. Extrapolating the decay curve, approximately 50 mg of residual caffeine at bedtime correlates with measurable increases in sleep-onset latency and reductions in total sleep time. This is a population average. Sensitive individuals may react to as little as 20 mg.

Pharmacokinetically, caffeine is caffeine regardless of source. The molecule (1,3,7-trimethylxanthine) is identical. However, tea contains L-theanine, which modulates the subjective experience by promoting alpha-wave brain activity. The absorption rate may also differ slightly due to tannins in tea binding caffeine, creating a slower release profile. The half-life and total metabolized amount remain the same.

No. The American College of Obstetricians and Gynecologists recommends limiting caffeine to under 200 mg/day during pregnancy. Caffeine half-life approximately triples in the third trimester (up to 15 hours) due to reduced CYP1A2 activity. Caffeine crosses the placenta freely, and the fetus lacks the enzymes to metabolize it. Set the sensitivity to "Low (slow metabolizer)" and halve the daily limit mentally when using this tool during pregnancy.

The calculator uses superposition: each dose starts its own independent decay curve from the time of consumption. This is pharmacologically valid for caffeine because it follows linear (first-order) kinetics at normal consumption levels (under ~500 mg). At very high doses (above 1 g), saturation kinetics may apply, and the model underestimates blood levels. For typical daily consumption patterns, the superposition model is clinically adequate.

The estimated LD50 for oral caffeine in humans is approximately 150 mg/kg body weight, which translates to roughly 10-12 grams for an average adult. However, fatalities have been reported at lower doses (5 g) in individuals with cardiac conditions. Caffeine powder and concentrated liquid supplements pose the highest risk because small measurement errors yield massive doses. This calculator flags intake above 10 mg/kg as a risk zone.