Free caffeine tracker
Know what's still with you before you pour another.
Log a drink and it'll show you what's on board now, what's left by the time the lights go out, and how late you can have the next one and still land under 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. What it can't do is sit on your home screen, nudge you at your curfew, or read your sleep from Apple Health. The iPhone app is free and does the first two.
Get the iPhone appTap one to log it. Each shows the latest you could have it and still land under your bedtime target. Once that time has gone by, it shows what it would leave you with instead.
A branded drinks list only knows what somebody has already measured, which is why they all miss your local roaster and your moka pot. The thing that travels between kitchens is milligrams per gram of dry coffee.
That works out at
These two mark out your night. Your day runs waking to waking as well, 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.
What the app adds
The web version does the maths. The iPhone app is the one you'll still be using in six months, and it's free.
One tap from the home screen
Your quick-add drinks sit on the widget as real buttons. Tap one, it's logged, the countdown updates in place, and the app never opens. That one detail is the difference between a tracker you use for a week and one you still have in a year.
A countdown on the lock screen
The lock screen widget is free. Pro adds the Live Activity and Dynamic Island countdown, so the time you drop back under your target is sitting right there, no digging for it.
A caffeine curfew alert
One notification, at the point where the next coffee would start eating into your night. Then a nudge in the morning you can long-press to rate how you slept, without opening anything.
Your sleep, from Apple Health
Connecting Health is free and works both ways: it reads your sleep and writes your drinks back as caffeine. Pro holds the nights you went to bed clear against the nights you didn't, shows you the pattern, and leaves the conclusion to you. It won't rewrite your half-life behind your back, because that data is far too tangled to trust with your warnings.
Free to use. Pro if you want the sleep half.
Logging, the dial, last call and the curfew alert are free forever, in the app and on the web. Pro adds the part about what caffeine has been doing to your sleep. No adverts anywhere in it.
Free
- Unlimited logging, app and widget
- The dial and the countdown to target
- Last call for every drink
- Caffeine curfew alert
- Morning and evening check-ins
- Home and lock screen widgets
- Brew calculator, all 7 methods
- Today and yesterday
- Apple Health, both ways
- Export your data
SlumberBrew Pro
- Your nights, compared
- Full history, charts and trends
- Live Activity and Dynamic Island
- Unlimited custom drinks
- All themes
Subscriptions are billed through your Apple Account and renew until you cancel, which you do in the App Store. If Pro lapses you keep every free feature, and nothing you logged is deleted. See the terms.
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.
Is the app free?
Yes, for the part you'll use every day. Logging, the dial, last call, the curfew alert, the widgets and the brew calculator are free forever, with no account and no adverts.
Pro is 99p a month or £6.99 a year, and adds the sleep analysis from Apple Health, full history and charts, the Live Activity countdown, unlimited custom drinks and the themes. If it lapses you keep everything free and nothing you logged is deleted.
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.