# Clearday: Caffeine & Sleep

> Clearday: Caffeine & Sleep (iPhone/iPad app by Takumi Kanzaki.)

- Source: https://appshunter.io/ios/app/clearday-caffeine-and-sleep/id6761060235 (this page in markdown: same URL + `.md`)
- Developer: [Takumi Kanzaki](https://appshunter.io/developer/1820952468)
- Category: Health & Fitness
- Price: Free with in-app purchases
- Age rating: 12+
- Requires: iOS 18.0 · 2 MB
- Languages: Japanese
- Released: 2026-03-26
- Data updated: 2026-07-17
- User reviews in markdown: https://appshunter.io/ios/app/clearday-caffeine-and-sleep/id6761060235/reviews.md

## What is Clearday?

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.

## Pricing and in-app purchases

Base price: Free.

**Subscriptions**

| Subscription | Price | Period |
| --- | --- | --- |
| Premium Monthly | $4.99 | per month |
| Premium Yearly | $34.99 | per year |



## Version history (last 1 release)

### 2.1 — 2026-03-31

# Japanese Language Support
Clearday is now available in Japanese! All screens, notifications, and widgets are fully localized. Your device language setting is automatically detected.

## More apps by Takumi Kanzaki

- [Kids Daily Checklist & Routine](https://appshunter.io/ios/app/kids-daily-checklist-and-routine/id6747349548)
- [おじいちゃんといぬ](https://appshunter.io/ios/app/id6747392810)
- [ChoresLogs&Allowance](https://appshunter.io/ios/app/choreslogs-and-allowance/id6747800793)
- [StrideMap: Step & Mile Tracker](https://appshunter.io/ios/app/stridemap-step-and-mile-tracker/id6748224869)
- [Lab Gone Wrong](https://appshunter.io/ios/app/lab-gone-wrong/id6748272674)
- [DepthDrift - Idle Cave RPG](https://appshunter.io/ios/app/depthdrift-idle-cave-rpg/id6748545569)

All apps by Takumi Kanzaki: https://appshunter.io/developer/1820952468

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-17.*