Caffeine Intake Calculator
Add up the caffeine in your day, see how much is left at bedtime and check it against the daily limit.
Your day
What you drank
Add at least one drink to see your caffeine total.
- Total caffeine today
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- Share of daily limit
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- Per kg of body weight
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- Still in you at bedtime
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- Drops below 50 mg at
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- Last safe caffeine time
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Breakdown
These numbers are estimates for general information only — not medical advice. Caffeine content varies a lot between brands, brew strengths and cup sizes, and how quickly you clear caffeine depends on genetics, medication, smoking and pregnancy. Talk to a doctor or midwife about your own limit.
How it works
The calculator adds up the caffeine in everything you logged, using a curated table of about 50 common drinks, chocolates and supplements with typical milligram values from the FDA, USDA and published brand figures. Because caffeine content genuinely varies — a home-brewed mug of coffee can be anywhere from 70 to 140 mg — treat every number as a good estimate rather than a lab measurement, and use the Custom amount option when you know the exact mg on the label.
To work out what is left later, it uses first-order elimination:
remaining = dose × 0.5 ^ (hours ÷ half-life). Caffeine's half-life in a healthy
adult averages about 5 hours, so 190 mg taken at 08:00 has halved three times by 23:00 and
leaves roughly 24 mg. The half-life picker lets you model a fast metaboliser (3 hours) or a
slow one (7 hours — closer to people on hormonal contraceptives or in pregnancy, where it can
be far longer still). "Drops below 50 mg" is the moment your estimated blood level passes a
commonly used sleep-friendly threshold, and the last safe caffeine time works backwards from
your bedtime so a single serving of your latest drink still clears that threshold.
Daily limits come from public guidance: 400 mg a day for healthy adults (US FDA and EFSA), 200 mg in pregnancy (ACOG and EFSA), 100 mg for adolescents, and 2.5 mg per kilogram of body weight for children. EFSA also considers single doses up to 200 mg unproblematic for adults, so the tool flags any one serving above that. Everything runs in your browser in plain JavaScript — nothing you type is uploaded, stored or shared, and there are no ads or sign-ups.
Frequently asked questions
How much caffeine per day is safe?
The US FDA and EFSA both put 400 mg a day as the level not generally associated with harmful effects in healthy adults — roughly four 8 oz cups of brewed coffee, or two and a half 16 oz energy drinks. EFSA adds that single doses up to 200 mg are unproblematic, so a 300 mg energy drink in one go is already above that. The guidance drops to 200 mg a day in pregnancy and breastfeeding (ACOG and EFSA), about 100 mg a day for adolescents aged 12–18, and 2.5 mg per kilogram of body weight for children under 12. Pick your profile in the calculator and it scores your total against the matching limit. These are population guidelines, not personal medical advice.
How long does caffeine stay in your system?
Caffeine is cleared by first-order elimination, so a fixed fraction disappears per unit of time: remaining = dose × 0.5 ^ (hours ÷ half-life). The average half-life in a healthy adult is about 5 hours, which means half is gone after 5 hours, three quarters after 10 and roughly 94% after 20. Two 8 oz coffees at 08:00 come to 190 mg, and by an 11 pm bedtime — exactly three half-lives later — about 24 mg is left. The half-life varies widely: 3 hours or less in fast metabolisers and heavy smokers, 6–7 hours or more for people on hormonal contraceptives, and far longer in the third trimester of pregnancy. The calculator lets you pick a 3 to 7 hour half-life so you can see the spread.
When should I stop drinking coffee before bed?
A common rule of thumb is to keep your estimated blood caffeine below about 50 mg by the time you go to sleep, and sleep studies have found measurable disruption from a dose taken as much as 6 hours before bedtime. Working backwards with a 5 hour half-life, a single 95 mg cup of coffee needs about 4 hours 38 minutes to fall to 50 mg, so an 11 pm bedtime means a last cup around 18:20; a 200 mg energy drink needs 10 hours. The tool shows both the amount still in you at bedtime and a last safe caffeine time for the strongest drink you logged, so you can set your own cut-off.