Fast Slow - Fasting Tracker

See what happens inside your body as you fast. Fast Slow walks you through 5 fasting zones, from digestion through fat burning to deep ketosis, so you understand what every hour of your fast is doing.

100% free. Every feature. No ads. No paywalls. No trackers. Free forever.

WHAT MAKES FAST SLOW DIFFERENT

Most fasting apps just count down a timer. Fast Slow shows you what's actually happening in your body at each stage:

• Anabolic (0-4h): Digesting and storing nutrients
• Catabolic (4-8h): Tapping into energy reserves
• Fat Burning (8-12h): The metabolic switch
• Ketosis (12-16h): Ketones and cellular cleanup
• Deep Ketosis (16h+): Deep cellular renewal

Tap any zone to learn more about the science behind it.

100% FREE. EVERY FEATURE INCLUDED.

No premium tier. No trial that expires. No paywall gates. Every feature in Fast Slow is yours from day one:

• All 6 fasting schedules
• All stats, streaks, and trends
• All widgets (Home Screen and Lock Screen)
• All notifications
• Siri Shortcuts
• iCloud sync
• Data export

Everything free. No catches.

FEATURES

Fasting Timer One tap to start. One tap to stop. A visual timeline shows where you are, what zone you're in, and what comes next.

6 Fasting Schedules 12:12 for beginners, 14:10, 16:8 (the most popular), 18:6, 20:4, and OMAD (one meal a day) for experienced fasters.

Visual Timeline Color-coded timeline of your fasting and eating windows. Plan meals, training, and recovery at a glance.

Smart Notifications 7 notification types: goal reached, halfway there, one hour left, eating window alerts, and a custom last meal reminder. Nudges, not nags.

Stats & Streaks Total fasts, average duration, personal records, weekly trends, and a monthly fasting calendar. Small wins add up.

Widgets Home Screen and Lock Screen widgets with progress rings, timelines, and live timers. Check your fast without opening the app.

Siri Shortcuts "Hey Siri, start my fast." Start, stop, and check your fasting status hands-free.

AI-Powered Greetings On supported devices, Apple Intelligence creates personalized messages based on your fasting progress, streak, and time of day.

iCloud Sync Your fasting data syncs automatically across all your devices.

Data You Own Export your fasting history as JSON. Delete everything with one tap. Your data, your choice.

DESIGNED FOR REAL LIFE

Pick a schedule, adjust as needed, and let Fast Slow handle the timing. New to fasting or already have a routine, it works either way. Structure when you want it, out of the way when you don't.

Built by one developer who fasts every day. No corporate agenda. No growth hacking. A well-made tool that respects your time and your data.

RESPONSIBLE APPROACH

Intermittent fasting can support weight management, energy, and focus, but results vary. Fast Slow provides tools and information, not medical advice. If you have health conditions, are pregnant, or have a history of eating disorders, please talk to a healthcare professional before starting.