Clearday: Caffeine & Sleep

Most caffeine apps tell you how much you've had. Clearday tells you what it's doing to your body.
Using your Apple Watch data — sleep score, resting heart rate, and HRV — Clearday calculates your personal caffeine cutoff: the latest time you can have a drink without wrecking your sleep.
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HOW IT WORKS
Caffeine has a half-life of 5–6 hours. That afternoon coffee at 3pm still leaves 25mg in your bloodstream at 11pm — silently reducing deep sleep. Clearday models this in real time, overlays your HealthKit data, and tells you exactly where your cutoff is.
No guesswork. Just your data.
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WHAT YOU GET
Blood-level curve
See your exact caffeine levels across 24 hours — past and predicted. A color-coded line at bedtime shows whether you're in the clear or heading for a rough night.
Personal cutoff card
After 7 days, Clearday analyzes your sleep scores against your caffeine timing to calculate your personal cutoff time. It updates as your data grows.
HealthKit correlation cards
- Sleep score — how your total and deep sleep shifts with caffeine intake
- Resting heart rate — 7-day trend overlaid with your logging history
- HRV — how caffeine-free days affect your heart rate variability
Withdrawal timeline (Quit & Reduce modes)
Breaking the habit? Clearday shows you a science-backed 9-day timeline — headaches typically peak at day 2, resolve by day 9 — so you know exactly what to expect and when it ends. Log symptoms in one tap and watch them ease off.
Three modes
- Optimize: Keep drinking coffee. Just stop at the right time.
- Reduce: Cut back gradually. Track how your body responds.
- Quit: Go caffeine-free. Clearday coaches you through withdrawal.
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BUILT ON SCIENCE
Clearday's caffeine decay model, cutoff calculations, and withdrawal timeline are based on peer-reviewed research published in Sleep Medicine Reviews, the New England Journal of Medicine, and the Journal of Clinical Sleep Medicine. Full references available in Settings → Science & References.
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PRIVACY
All HealthKit data stays on your device. Clearday reads sleep, resting heart rate, and HRV — and never shares it with anyone.
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PREMIUM
Unlock HealthKit correlation cards, personal cutoff insight, withdrawal timeline, and home screen widgets with a Premium subscription.
$4.99/month or $34.99/year. Cancel anytime.
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From the developer of Soberday: Alcohol & Sleep.