Intermittent Fasting Timer
Choose your fasting protocol, set your last meal time, and see exactly when your eating window opens and what fasting zone you are in.
Common Fasting Protocols
16:8 is the most popular protocol. Fast for 16 hours, eat during an 8-hour window (typically noon to 8 PM). Good for beginners. 18:6 is a slightly more aggressive version with a 6-hour eating window. 20:4 (also called the Warrior Diet) limits eating to a 4-hour window. OMAD (One Meal a Day) is the most extreme daily fasting protocol, eating during a 1-hour window. 14:10 is the gentlest protocol, often recommended as a starting point.
What Happens During a Fast
During the first 4 hours, your body is still digesting your last meal. From 4-8 hours, blood sugar and insulin levels drop as stored glycogen is used. Around 8-12 hours, glycogen stores deplete and the body begins burning fat for fuel. After 12-18 hours, ketone production increases significantly. After 18-24 hours, autophagy (cellular cleanup and recycling) ramps up. These timelines are approximate and vary based on your metabolism, activity level, and what you ate before the fast.
Fasting FAQ
What can I consume during a fast?
Water, black coffee (no sugar, cream, or milk), and plain tea are generally considered acceptable during a fast. Anything with calories, including sugar-free drinks with artificial sweeteners, may trigger an insulin response and partially break the fast. The strictest interpretation allows only water.
Is intermittent fasting safe?
For most healthy adults, intermittent fasting is safe and well-studied. It is not recommended for children, pregnant or breastfeeding women, people with a history of eating disorders, people with type 1 diabetes, or those taking medications that require food. If you have any medical conditions, consult your doctor before starting.
Does fasting cause muscle loss?
Short-term fasting (16-24 hours) with adequate protein intake during eating windows does not cause significant muscle loss in most people. Research shows that combining intermittent fasting with resistance training preserves muscle mass effectively. Extended fasting beyond 24-48 hours without exercise does increase the risk of muscle breakdown.
Will fasting slow my metabolism?
Short-term intermittent fasting does not slow metabolism. Some research suggests it may slightly increase metabolic rate in the first 24-48 hours due to norepinephrine release. Chronic severe calorie restriction (regardless of timing) can reduce metabolic rate over time, but this is related to total calorie intake, not meal timing.