Stages, not streaks.
Track the biochemical arc of a 24 to 72+ hour fast with phase-aware timing, ketone logging, and private session records. Built for biohackers running protocols, not counting calories.
Most fasting apps optimize the 16:8 newbie.
Fast36 is for the 24h-to-5-day crowd — self-experimenters running protocols, measuring ketones, tracking autophagy.
Preset durations
24 / 36 / 48 / 72 hour presets tuned to fasting physiology, not arbitrary round numbers.
Real-time stages
Glycogen depletion, ketosis, autophagy, deep autophagy — narrated minute by minute as you cross each threshold.
Live Activity + Dynamic Island
Your Lock Screen becomes the instrument. A glance shows stage, ring, and time to the next phase.
Local history
Every fast is saved on-device. No cloud, no sync, no leaderboards. Your body data stays yours.
Stages, not streaks.
Each stage is different biochemistry. Fast36 tells you what’s happening in your body — and when the next phase begins.
Glycogen Depletion
Your body burns stored carbs from the liver. Insulin and blood sugar drop as glycogen runs down.
Ketosis
Glycogen depleted. The liver produces ketones from fat. Energy shifts from glucose to fat metabolism.
Autophagy
Cellular cleanup accelerates. Cells recycle damaged proteins and organelles — the process Ohsumi won the 2016 Nobel Prize for.
Deep Autophagy
Growth hormone spikes, autophagy peaks, stem cell regeneration ramps up. This is where extended fasting earns its reputation.
Free to run a 36-hour fast. Pro for everything else.
Try the app free. Unlock extended protocols, Live Activity, Watch, Science, and more when you’re ready.
The namesake 36-hour protocol, real-time stages, and local history. No account, no ads.
- 36-hour fasts
- Real-time stage tracking
- Local history
- Home Screen widget
Shorter resets, longer arcs, and the full instruments — Live Activity, Watch, Science, and more.
- 24h / 48h / 72h protocols
- Live Activity + Dynamic Island
- Apple Watch app
- The Science reference
- Stage distribution history
- Apple Health sync
- Haptic stage crossings
- Notes per fast
Cancel anytime · On-device data · No ads, ever
Fast36 on iOS.
Ships on iPhone, iPad, and Apple Watch. Join the waitlist for the TestFlight invite, or reserve your copy on the App Store now.