Free caffeine tracker
See what's still in your system before you pour another.
Log a drink and see what's in your system now, what's left at bedtime, and how late you can have another without going over your target.
It all stays in this browser. No account, nothing sent anywhere.
Today's log
This is the browser version
Same model, same numbers. The iPhone app is coming soon; until then, this browser tracker is here whenever you need it.
Get the appTap one to log it. Each shows the latest you can have it and stay under your bedtime target. Past that time, it shows what it would leave you with instead.
A branded drinks list only knows what someone has already measured, which is why they all miss your local roaster and your moka pot. The number that actually carries across kitchens is milligrams of caffeine per gram of dry coffee.
That works out at
These two set your night. Your day runs wake-up to wake-up too, so a coffee at 11pm counts towards the day that's ending.
Measured half-lives run from under 3 hours to nearly 10. Oral contraceptives roughly double it, smoking roughly halves it. If a coffee in the early afternoon reliably wrecks your night, slide this up.
The lowest single dose with published sleep effects is around 100mg, so keep the target well under that. The daily limit just sets the scale of the dial. Neither one is a medical safety line.
Your data
Everything here is stored in this browser and nowhere else. Clearing your browser data removes it. We never see it.
The number arrives before the cup, not after
Most caffeine apps are a diary. You log the coffee, they add it up, and you find out you overdid it somewhere around midnight, by which point knowing is no use to anybody.
Last call, per drink
Every drink carries the latest time you could have it and still land under your bedtime target. Once that time has gone, the row swaps the time for the number it would leave you with: "227mg overnight". You see it before you tap, while it's still a choice.
Set to your metabolism
Measured caffeine half-lives run from under 3 hours to nearly 10 across healthy adults. That's the gap between a 2pm espresso being long gone by bed and half of it still hanging about. So it's a slider, not a constant.
Work it out from the brew
Filter, espresso, AeroPress, moka, French press, cold brew or instant. By weight of coffee, or by water and ratio. It answers with a range, because the same drink measured across twenty coffee shops varied sixfold.
The model is one-compartment pharmacokinetics with first-order absorption: caffeine climbs for about half an hour before it starts coming back down. Treat a dose as instant and you overstate the first hour by about a third, which is how an espresso gets waved through at lights out.
Questions
Why does it give me a range instead of a number?
Because a number would be a lie most of the time. A study measuring the same espresso order across twenty coffee shops found a roughly sixfold spread, and a home drip coffee can land at half or double the figure in any catalog. Being precise about the uncertainty beats being confidently wrong.
Where does my data go?
Nowhere. The web version keeps everything in your browser's local storage. The app keeps everything on your phone. There's no account, no server and no analytics on this site. See the privacy policy.
Can it tell me my own half-life?
No, and it won't guess either. A bad night could be caffeine, or a late meal, or a noisy street, or a stressful week. Rewriting the model your warnings are built on from data this tangled would make the warnings worse while looking like a feature. So you set it: oral contraceptives roughly double half-life, smoking roughly halves it.
So is caffeine still in my system a bad thing?
No. Caffeine sitting in you overnight isn't dangerous and this isn't a warning light. It's only that caffeine near bedtime tends to cost you sleep: in Drake's 2013 study, 400mg six hours before bed cost people over an hour of it. Your bedtime target is a number you choose for how much you'd rather not have on board when you turn in. Everything on this page is measured against that.
Is this medical advice?
No. SlumberBrew isn't a medical device and doesn't diagnose or treat anything. It's an estimate built on published averages, and the averages may not describe you. If you have a health condition, take medication, are pregnant, or are worried about caffeine or your sleep, talk to a doctor and go with what they say.
Where do the numbers come from?
Four papers do most of the work, and the app links every claim back to its source:
- Blanchard & Sawers 1983, for half-life range, time to peak and bioavailability
- Nehlig 2018, for why half-life varies between people
- Drake et al. 2013, for 400mg six hours before bed costing over an hour of sleep
- EFSA 2015, for the 400mg daily and 200mg single-dose guidance
If a claim can't be sourced, it isn't in the app.