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Caffeine calculator

Log your drinks and see your daily caffeine total and estimated level at bedtime.

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Caffeine calculator
Paste a list of the drinks you had today, one per line, in the format "drink, time" — for example "Espresso, 08:00" or "Filter coffee, 10:30, 2" for two cups. The tool looks each drink up in a built-in table (espresso, filter coffee, instant coffee, energy drink, cola, tea, green tea, matcha, decaf and hot chocolate) and adds up how much caffeine you consumed and when.
The result shows your total daily intake compared with the commonly cited 400 mg guideline for healthy adults, plus an estimate of how much caffeine is still active in your system at bedtime. That estimate uses caffeine's roughly five-hour elimination half-life: every drink's contribution is halved for each half-life that passes between when you drank it and your bedtime. Adjust the "Bedtime" and "Caffeine half-life" options to match your own schedule and metabolism — half-life varies a lot between individuals and can range from about three to seven hours.
Don't see your drink in the table? Set "Custom drink name" to whatever you typed on that line and "Custom drink mg per serving" to its caffeine content, and it's picked up like any built-in entry. A line the tool can't read — a misspelled drink or a time that isn't in HH:MM format — is listed separately as unrecognized rather than breaking the rest of the calculation, so the parts it did understand are always usable.
Everything runs locally in your browser: nothing you type is uploaded anywhere. Copy the report, download it as a .txt file, or send it straight to another tool's input once you're done. This tool gives general estimates based on published averages, not medical advice — individual caffeine sensitivity and metabolism vary.
FAQ
How is the caffeine level at bedtime calculated?
Each drink's caffeine is assumed to decay exponentially with the half-life you set (default 5 hours). A drink consumed after your bedtime doesn't count toward the estimate, since it hasn't been consumed yet at that point in your day.
Where do the built-in mg values come from?
They are commonly cited averages per typical serving — actual caffeine content varies by brand, brew strength and serving size, so treat them as estimates rather than exact measurements.
What happens to a drink or time it doesn’t recognize?
That line is listed under "Not recognized" instead of being silently dropped or blocking the rest of the log, so you can fix the spelling or format and re-check it.
Can I add a drink that isn’t in the built-in table?
Yes. Set the custom drink name and its mg per serving in the options, then use that same name on any line in your log.
Is my caffeine log uploaded anywhere?
No. The calculation runs entirely in your browser — what you type never leaves your device.