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Plan your intermittent fasting schedule with eating and fasting windows for 16:8, 18:6, OMAD, and more.
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.
Calculate your exact eating and fasting windows for any IF protocol, track your fast, and understand the benefits of each stage.
Select your fasting protocol (16:8, 18:6, etc.).
Set your eating window start time.
See your exact fasting and eating windows.
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.