Fast36

Stages, not streaks.

Fast36 is the fasting app for people who care about the metabolic arc, not the calendar grid. Track the biochemical progression of a 24 to 72+ hour fast with phase-aware timing, in-the-moment science, and a private record of every session.

WHAT YOU GET

• Stage-aware timer. Watch your fast move through the four metabolic regimes — glycogen depletion, ketosis, autophagy, deep autophagy — with color-coded thresholds that match real human physiology.

• Quick Log for ketones and glucose. Pair every fast with a finger-stick reading. Build a longitudinal record of how your biomarkers respond to each protocol.

• Live Activity on the Lock Screen. Current stage, elapsed time, and next threshold — always one glance away. No need to open the app.

• Apple Watch companion. Start, monitor, and end fasts from your wrist. Phone, iPad, and watch always show the same session.

• History with substance. Total hours, per-stage distribution, per-fast gantt, readings, notes. No streaks. No flame emoji. No celebratory confetti.

• The Science reference. Peer-reviewed citations for every stage claim. We tell you what's proven in humans and what's extrapolated from rodent studies, and when evidence is emerging rather than settled.

FREE

• 36-hour protocol — the namesake fast
• Stage-aware timer and Stages reference
• History log and HealthKit integration
• On-device privacy

FAST36 PRO — $14.99 / month or $99 / year

• 24-hour reset fasts
• 48-hour and 72-hour extended protocols
• Custom fast lengths
• Live Activity with stage transitions
• Stage-crossing haptics
• Apple Watch companion
• Quick Log for ketones and glucose
• Full history analytics and stage distribution chart
• Notes on every fast
• Apple Health bidirectional sync
• The Science deep-dive with citations

WHO IT'S FOR

Biohackers running 24 / 36 / 48 / 72-hour protocols. People who want their fasting app to read like a lab notebook, not a game. Anyone who has ever said "autophagy" at dinner and meant it. Not for calorie counting, not for weight-loss streaks, not for "gamified wellness."

PRIVACY

All fasting data lives on-device. Optional Apple Health sync stays between you and Apple — it does not pass through our servers. No accounts, no newsletters, no behavioral tracking, no third-party analytics.

Not medical advice. Extended fasting carries real risks for people with diabetes, eating disorder history, pregnancy, low body fat, or on medications affecting blood sugar or blood pressure. Consult a clinician before attempting any fast over 24 hours.

Fast36 Pro subscriptions renew automatically unless cancelled at least 24 hours before the current period ends. Manage or cancel from your Apple ID settings.

Terms of Use: https://fast36.app/terms
Privacy Policy: https://fast36.app/privacy
Support: hello@fast36.app