Intermittent fasting duration calculator
Enter when you last ate and your fasting protocol. See exactly when your fast ends and how much time remains.
Common fasting protocols
- 16:8 — Fast for 16 hours, eat within an 8-hour window. The most popular protocol; compatible with most lifestyles when the eating window is set at noon–8 PM.
- 18:6 — A stricter variant; 18-hour fast leaves a 6-hour eating window. Popular with experienced IF practitioners.
- 20:4 (Warrior Diet) — 20-hour fast with a 4-hour evening eating window. Often involves one large meal.
- OMAD (One Meal A Day) — A 23–24 hour fast. Effective for weight loss but requires attention to nutrient density in the single meal.
- 36 hours — An extended fast, typically done once or twice per week (e.g., 5:2 protocol). Consult a doctor before attempting.
What breaks a fast?
Caloric intake breaks a fast. Water, black coffee, and plain tea are generally considered fast-safe. Milk, cream, sugar, or any caloric addition ends the fast. Some practitioners also allow zero-calorie electrolytes for extended fasts.
Track your fast with Left
Add your fast end time as a countdown in Left. The widget on your Lock Screen will show you exactly how much fasting time remains — without needing to open an app or do the mental math.
Start noticing what matters.
Download Left on your iPhone to see the time you have left, dates you are looking forward to, build the habits you want to keep, and become a better version of yourself.
Scan with your camera to find Left on the App Store. Or search "Left" on the App Store.