Stack - Caffeine & Sleep

Precise. Personal. Science-backed.

Stack is your personal biohacking dashboard — caffeine, sleep, water, supplements, and alcohol in one app.

HOW IT WORKS Caffeine breaks down exponentially at an individual half-life. Stack calculates your current level from everything you've consumed: espresso, filter coffee, matcha, energy drinks, pre-workout.

YOUR SLEEP WINDOW Instead of a fixed cutoff, Stack learns your personal threshold — the caffeine level below which you sleep well. Set your bedtime. Stack tells you if and when you'll be below it tonight.

AUTO-CALIBRATION WITH APPLE HEALTH (PRO) Have an Apple Watch? Stack analyzes your heart rate variability (HRV) and resting heart rate relative to your caffeine level and calculates your true personal half-life. The more nights, the more precise the model.

SLEEP INSIGHTS (PRO) How much deep sleep do you lose when caffeine is still in your blood at bedtime? Stack shows you the correlation from your own sleep data — not general studies, but your nights.

WIDGET Caffeine level directly on your home screen — small, medium, or as a lock screen widget.

YOUR DAILY STACK Stack tracks water, creatine, and supplements — and shows you when alcohol is additionally affecting your sleep. Everything in one place, without distraction.

YOUR DATA STAYS YOURS No account. No cloud. All data stays on your iPhone. Apple Health is optional and used exclusively on-device.

Stack Pro unlocks: Auto-Calibration · Sleep Insights · Health Dashboard · Notifications · Custom Presets · Tolerance Analysis

Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/