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Fasting Protocol
Eating Window
12:00 PM – 8:00 PM
8h window
Fasting Window
8:00 PM – 12:00 PM
16h fast
Suggested Meal Times
24-Hour Timeline
Intermittent Fasting Calculator calculates exact eating and fasting windows for any IF protocol (16:8, 18:6, 20:4, OMAD, 5:2, alternate-day) from your chosen start time, shows which metabolic phase your body enters over the fast, and includes a live fast timer.
Intermittent Fasting Calculator is a high-performance utility designed to help users streamline their workflow. Built with modern web technologies, it ensures fast processing times and high-quality outputs directly in your browser.
Fasting windows calculated from user-defined eating start time plus protocol hours. Metabolic phase timeline: 0–4h (digestion), 4–8h (glycogenolysis), 8–12h (gluconeogenesis begins), 12–16h (ketosis entry), 16–24h (autophagy activation).
16:8 (fast 16 hours, eat within an 8-hour window) is the most widely practiced protocol.
Glycogen stores deplete after 12–16 hours of fasting, after which the body shifts to burning fat.