Caffeine Calculator
Calculate how long caffeine stays in your body. See the remaining amount after each half-life and when it is safe to sleep. Includes a sources table (coffee, tea, energy drinks, chocolate). Everything in your browser.
Não sabe?
5h é a média em adultos saudáveis. Gestantes: 10–15h. Fumantes: 3–4h.
Após 1 meia-vida
0 mg
em 0h
Após 2 meias-vidas
0 mg
em 0h
Seguro para dormir
0h
após o consumo (cafeína < 50 mg)
Eliminação quase completa
0h
~3% restante (5 meias-vidas)
Como funciona
A cafeína obedece a uma cinética de eliminação de primeira ordem, ou seja, a cada meia-vida a quantidade no sangue cai pela metade. Em adultos saudáveis a meia-vida média gira em torno de 5 horas, mas a variação é grande. Gestantes ficam na faixa de 10–15h, fumantes em 3–4h, e quem tem certas mutações no gene CYP1A2 também sai da média.
Quem quer dormir bem geralmente mantém a cafeína abaixo de 50 mg na hora de deitar. A fórmula por trás disso é restante = inicial × 0,5^(t / meia-vida). O cálculo roda inteiro no seu navegador.
Caffeine half-life and safe dose
Caffeine follows first-order pharmacokinetics, which means the blood concentration drops by half at each half-life. For healthy adults the population average sits around 5 hours (somewhere between 3 and 7 h), but pregnancy stretches that out two or three times over (10–15 h), and smokers clear it faster (3–4 h). The decay equation is remaining = initial · 0.5^(t / half-life). Take an example: drink 200 mg at 18:00 and you're left with roughly 100 mg at 23:00, 50 mg at 04:00, and only about ~6 mg by 13:00 the next day. The safe ceiling for healthy adults is 400 mg/day (FDA, EFSA). Pregnant people should keep it under 200 mg/day given the risk of miscarriage and low birth weight, and for children the figure is around 2.5 mg/kg. Where it shows up: espresso runs ~63 mg per 30 mL, drip coffee ~95 mg per 240 mL, energy drinks 80–300 mg, cola sodas 30–40 mg, and dark chocolate 20–60 mg per 100 g.
Genetics, tolerance and sleep
In the brain, caffeine blocks adenosine receptors, and that holds back the signal that builds sleep pressure. About 95% of caffeine metabolism runs through the liver enzyme CYP1A2, and a single-nucleotide polymorphism sorts people into two camps. Fast metabolizers (AA homozygotes) see less of a hit to their sleep from coffee, while slow metabolizers (AC/CC) carry higher cardiovascular risk when they drink a lot. Use caffeine every day and the brain up-regulates those adenosine receptors, so you build tolerance to the alertness boost, though not entirely to the sleep disruption. A couple of practical pointers: for an ergogenic effect, take 3–6 mg/kg about 30–45 minutes before training, and stop all caffeine at least 6 hours before bedtime. Research found that even 400 mg taken 6 h before bed cuts total sleep by roughly an hour.
FAQ
Why do I sleep fine after coffee? You might be a fast CYP1A2 metabolizer, or you've built up tolerance in your adenosine receptors. Even so, objective measures like deep sleep and HRV often still look worse, even when the sleep feels normal to you.
Does decaf have caffeine? It does. A cup usually carries 2–15 mg. That's small, but it isn't zero.
How long do withdrawal symptoms last? The headache, fatigue and irritability tend to peak 24–48 h after you stop and clear up within 7–9 days. Tapering off slowly keeps them from showing up at all.
Is caffeine dangerous? Acute toxicity is rare and generally takes more than 10 g, roughly 100 cups of coffee. With moderate intake the downsides are mostly anxiety, palpitations, GERD and disrupted sleep, and all of those are reversible.
Related Tools
Rent Adjustment Calculator
Compute annual rent adjustment by IGP-M or IPCA accumulated in the last 12 months (manually configurable).
Pregnancy Calculator
Compute estimated due date (EDD), gestational age and trimester from the last menstrual period (LMP).
Fertile Period Calculator
Compute fertile window and ovulation day from the first day of the last cycle and the average cycle length.
How long caffeine stays in your body
That late-afternoon coffee might be exactly why you keep tossing and turning. Caffeine has a half-life of a few hours, so half the dose is still circulating long after your last sip. This calculator draws out that curve and helps you plan your intake with a bit more sense.
Type in the dose and the time. From there the tool works out how much caffeine is left after each half-life, plus the point where you can sleep without it interfering. There's also a table of caffeine in everyday sources, like coffee, tea, energy drinks and chocolate, so you can ballpark how much you've already had.
Whatever you enter stays put, since the math runs right in your browser and nothing is stored. Handy for people who are sensitive to caffeine but still want the lift without wrecking their sleep.