Caffeine, sleep, and the gap between them
You know coffee too late wrecks your sleep. You don't know if this one counts.
SlumberBrew works out what's still in you and what will be left when your head hits the pillow. Then it tells you the latest you could have another and still be fine.
The web version is free and needs no account. Nothing you log leaves your browser.
This is the real model, running live. Watch a 2pm coffee play out against a 10pm bedtime.
The warning comes before the drink, not after
Most caffeine apps are a diary. You log the coffee, they add it up, and you find out you overdid it once it's too late to matter.
Last call, per drink
Every drink shows the latest time you could have it and still hit your bedtime target. Past that, it stops showing a time and starts showing the damage: "227mg at bed". You see it before you tap.
Set to your metabolism
Measured caffeine half-lives run from under 3 hours to nearly 10 across healthy adults. That's the difference between a 2pm espresso being gone by bed and it being half there. So it's a setting, 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 to fall. Treating a dose as instantaneous overstates the level by a third in the first hour, and would happily wave through an espresso at lights-out.
What the app adds
The web version does the maths. The iPhone app makes it something you'll actually keep up with, and it's free to use.
One tap from the home screen
Your quick-add drinks sit on the widget as real buttons. Tap one and it's logged, the countdown updates in place, and the app never opens. That's the whole difference between a tracker you use for a week and one you use for a year.
A countdown on the lock screen
The lock screen widget is free. Pro adds a Live Activity and Dynamic Island countdown, so how long until you're clear is there without you going looking for it.
A caffeine curfew alert
One notification at the moment your next coffee would start costing you sleep. Plus a morning nudge you can long-press to rate last night without opening anything.
Your sleep, from Apple Health (Pro)
Connect Health and the app lines up caffeine at bedtime against how you actually slept. It shows you the pattern and lets you draw the conclusion. It won't quietly rewrite your half-life from it, because that data is far too confounded 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 what caffeine has been doing to your sleep. No advertising in any of it.
Free
- Unlimited logging, app and widget
- The dial and sleep-safe countdown
- Last call for every drink
- Caffeine curfew alert
- Home and lock screen widgets
- Brew calculator, all 7 methods
- Today and yesterday
- Export your data
SlumberBrew Pro
- Your sleep, from Apple Health
- Morning sleep rating
- 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 be half or double the figure in any catalog. Being precise about the uncertainty is more useful than 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 advertising.
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 deliberately won't guess. A bad night could be caffeine, or a late meal, or a noisy street, or a stressful week. Silently rewriting the model your warnings are built on, from data that confounded, would make the warnings worse while looking like a feature. Set it yourself: oral contraceptives roughly double half-life, smoking roughly halves it.
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 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.