Track your daily caffeine, see it decay in your body hour by hour, find your last-coffee cutoff before bed, check your personal safe limit, browse a 64-drink caffeine database — and check caffeine toxicity for dogs & cats.
⚠️ Estimates, not medical advice. Caffeine content varies 30%+ by brand, beans, and brew — figures here are researched estimates (many anchored to USDA FoodData Central), not lab measurements. Half-life varies by person. The 400 mg/day (adult) and 200 mg/day (pregnancy) figures are FDA/EFSA population limits, not personal recommendations. Talk to your doctor about health decisions, and call an emergency vet immediately if a pet ingests caffeine.
1 · Caffeine Intake Tracker
Log what you drink today — total milligrams update live, and the half-life visualizer below uses your log automatically. Saved in your browser only.
0 mg logged today
Estimated caffeine still in your body right now0 mg
Items logged0
2 · Half-Life Decay Visualizer
One curve from all your logged drinks (first-order elimination: C(t) = C₀ × 0.5t / half-life). Adjust your half-life — peak absorption is ~30–60 min in real life; this model shows post-absorption decay.
In body now: 0 mgIn 6 h: 0 mgCleared under 5 mg at: —
Why the curve matters: a 200 mg coffee at 8:00 AM still leaves ~100 mg at 1:30 PM and ~25 mg at 10:30 PM for an average metabolizer.
3 · Sleep Cutoff Solver
Enter your bedtime — the solver answers “when is my last coffee?” so body caffeine falls under your chosen threshold by lights-out. t = half-life × log2(dose ÷ target). Wondering how much caffeine is in my system at bedtime? This solves it.
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Even 100 mg taken 6 hours before bed has been shown to reduce sleep — the 25 mg default is the conservative, sleep-friendly choice. Your personal caffeine cut off time is computed from your dose, half-life, and target; individual sensitivity varies.
Limits are population guidance from FDA/EFSA — not personal medical advice. People with heart conditions, anxiety, or on medication should talk to a doctor; some should avoid caffeine entirely.
5 · Caffeine Content Database — 64 Drinks
Every drink by brew method with mg per serving and mg per 100 ml. Many coffee values anchored to USDA FoodData Central; chain drinks from published nutrition info.
Sort:
Drink
Serving
mg
mg/100 ml
Note
☕ Light vs dark roast — the myth: by weight, roast level barely changes caffeine. By scoop, light roast packs slightly more caffeine because light-roasted beans are denser. “Dark = stronger” is about flavor, not caffeine.
6 · Pet Caffeine Toxicity Checker
Caffeine is toxic to dogs and cats. Estimate mg per kg from what was ingested — then call your vet regardless of the result.
— mg/kg—
🚨 EMERGENCY: If your pet swallowed coffee, tea, energy drinks, caffeine pills, or coffee grounds — call your veterinarian or emergency animal poison hotline IMMEDIATELY. Signs (vomiting, restlessness, rapid heartbeat, tremors, collapse) can start within 30–60 minutes. Do not induce vomiting unless a vet tells you to. This checker estimates risk; it is not a diagnosis and never replaces emergency care.
Reference thresholds (caffeine, mg/kg): dogs — signs from ~20, serious from ~50, potentially fatal near 100. Cats are roughly twice as sensitive (~10 / ~25 / ~50). Chocolate adds theobromine on top of caffeine — treat chocolate ingestion as more dangerous.
Methodology & sources
Decay model: first-order elimination, C(t) = C₀ × 0.5^(t / half-life), default half-life 5.5 h (average adult). Superposition across all logged doses.
Sleep cutoff: solves t = half-life × log₂(dose / target); default target 25 mg at bedtime.
Drink data: coffee/tea staples anchored to USDA FoodData Central (brewed coffee 95 mg/8 oz; espresso 63 mg/shot; black tea 47 mg; green tea 28 mg); chain drinks from published brand nutrition; energy drinks from can labels. Treat all as estimates — actual content varies 30%+.
Pet thresholds: veterinary toxicology references (caffeine methylxanthine toxicity): dogs mild ~20, moderate ~50, severe ~100 mg/kg; cats ~2× more sensitive.
Privacy: 100% client-side — your log is stored only in this browser's localStorage; nothing is sent anywhere.
Frequently asked questions
What is the half-life of caffeine?
Caffeine's half-life averages about 5.5 hours in healthy adults — after 5.5 hours half is cleared, after 11 hours a quarter remains. It ranges from about 3 hours (fast metabolizers, smokers) to 7 hours (slow metabolizers) and up to about 10 hours in late pregnancy. Use the half-life visualizer above with your own preset.
How long does caffeine stay in your system?
Roughly five half-lives to clear almost all of it: about 27 hours for an average adult after one dose. A 200 mg cup at 8:00 AM leaves about 100 mg by 1:30 PM and about 25 mg around 10:30 PM. The decay curve above shows your personal timeline.
When should I stop drinking coffee before bed?
Enter your bedtime in the sleep cutoff solver — it solves t = half life × log2(dose ÷ target). A common rule is keeping body caffeine under about 25 mg at bedtime. For a 300 mg dose with average metabolism that is roughly 19–20 hours — which is why an afternoon coffee can still disturb sleep.
How much caffeine per day is safe?
The FDA and EFSA consider up to 400 mg per day safe for healthy adults — about 4 cups of brewed coffee. During pregnancy or while breastfeeding, EFSA advises staying under 200 mg per day. These are population limits, not personal medical recommendations.
Is there a caffeine limit by body weight?
For children, EFSA suggests a maximum of 2.5 mg per kg of body weight per day. For adults the fixed 400 mg/day FDA/EFSA limit applies; the safe-limit module personalizes it by weight, age group, pregnancy, and breastfeeding.
How much caffeine is safe during pregnancy?
EFSA advises no more than 200 mg of caffeine per day during pregnancy — about two small cups of coffee — and notes caffeine's half-life can stretch to about 10 hours in the third trimester. Always confirm with your own doctor.
How much caffeine is in coffee, espresso, and cold brew?
Per USDA-published values: 8 oz brewed coffee ≈ 95 mg; a 1 oz espresso shot ≈ 63 mg; a 16 oz diluted cold brew ≈ 200 mg. The drink database above lists 64 drinks by brew method with mg per serving and per 100 ml.
Does light roast or dark roast have more caffeine?
By weight, roast level barely changes caffeine content. By scoop, light roast packs slightly more caffeine because light-roasted beans are denser. The dark = stronger myth comes from flavor, not caffeine.
How does coffee caffeine compare to tea, matcha, and energy drinks?
8 oz brewed coffee (95 mg) beats black tea (47 mg) and green tea (28 mg); matcha (70 mg) sits between coffee and tea; a 16 oz Monster (160 mg) out-caffeines most coffees, while a Bang or Reign (300 mg) tops them all.
How much coffee is 300 mg of caffeine?
About three 8-oz cups of brewed coffee, five espresso shots, or one 16-oz Starbucks Pike Place (310 mg). The safe-limit module converts your limit into cups of any drink in the database.
Is caffeine toxic to dogs and cats?
Yes. Dogs can show toxicity from about 20 mg/kg (vomiting, restlessness), serious effects from about 50 mg/kg, and doses near 100 mg/kg can be fatal. Cats are roughly twice as sensitive. If your pet swallowed caffeine, call an emergency vet immediately; this tool is not a substitute for emergency care.
What is caffeine sensitivity — fast vs slow metabolizer?
Sensitivity is mostly genetic (CYP1A2 enzyme speed). Fast metabolizers clear caffeine with about a 3-hour half-life; slow metabolizers take about 7 hours. Smoking shortens half-life; oral contraceptives lengthen it to about 8 hours.
What are caffeine withdrawal symptoms?
Headache, fatigue, irritability, and difficulty concentrating, typically starting 12–24 hours after the last dose and peaking at 1–2 days. Tapering gradually (about 25% less every few days) is gentler than quitting cold turkey.
Does decaf coffee have caffeine?
Yes, a little: about 2–7 mg per 8-oz cup (we use 4 mg). Decaf is not caffeine-free — relevant if you are counting milligrams for sleep or pregnancy.
How is caffeine content measured per 100 ml?
mg per 100 ml = (mg per serving ÷ ml per serving) × 100. Espresso is the most concentrated (about 210 mg/100 ml); brewed coffee is around 40 mg/100 ml.
How accurate is this caffeine calculator?
Caffeine content varies 30% or more between brands, bean batches, and brews — these are researched estimates (many anchored to USDA FoodData Central), not lab measurements. Half-life varies by person. This tool is for education and planning, not medical advice; consult a doctor for health decisions and a vet for pet emergencies.
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