Clearday: Caffeine & Sleep
by Takumi Kanzaki
· Health & Fitness
· Free
On the App Store since March 2026
· Data updated
Clearday: Caffeine & Sleep is made and published by Takumi Kanzaki. AppBrain is an independent app data site and isn't affiliated with Takumi Kanzaki. The app name, icon, screenshots and description belong to Takumi Kanzaki and are shown as published on the App Store.
AppBrain's verdict
- Last updated
- November 1, 2026
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Releases
Updates seen on the App Store- Version
- 2.2
- Launched
- March 2026
No changelog data
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Technology
Found in the app by AppBrain- Price
- Free
- App size
- 2.33 MB
- Content rating
- Medium
Technologies used by Clearday: Caffeine & Sleep
About the app and developer
About Clearday: Caffeine & Sleep
Clearday: Caffeine & Sleep is a health & fitness app developed by Takumi Kanzaki.
What is the rating of Clearday: Caffeine & Sleep?
Clearday: Caffeine & Sleep has no ratings yet.
Is Clearday: Caffeine & Sleep free?
Clearday: Caffeine & Sleep is free. The app size is 2.33 MB. The latest version available is 2.2. The last update was on November 1, 2026.
What are the requirements for Clearday: Caffeine & Sleep?
The app has a content rating of Medium Maturity. The app has been available on the App Store since March 2026.
Developer information for Takumi Kanzaki
Address:
Store listing
By Takumi Kanzaki, from the App Store
Screenshots by Takumi Kanzaki, from the the App Store listing
Description by Takumi Kanzaki Written by the developer, not by AppBrain. Click to read.
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.
—
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.
—
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.
—
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.
—
PRIVACY
All HealthKit data stays on your device. Clearday reads sleep, resting heart rate, and HRV — and never shares it with anyone.
—
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.
—
From the developer of Soberday: Alcohol & Sleep.
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.
—
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.
—
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.
—
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.
—
PRIVACY
All HealthKit data stays on your device. Clearday reads sleep, resting heart rate, and HRV — and never shares it with anyone.
—
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.
—
From the developer of Soberday: Alcohol & Sleep.