Intermittent Fasting Calculator

Intermittent fasting (IF) cycles between periods of eating and fasting. The most popular approach is 16:8: fast for 16 hours, eat within an 8-hour window. This naturally reduces calorie intake for most people, improves insulin sensitivity, and may have cellular health benefits through a process called autophagy.

Start with 12:12 (12 hours fasting, 12 hours eating) — this is barely different from not eating after dinner. Progress to 14:10, then 16:8 as your body adapts. Most people find 16:8 sustainable long-term. Skipping breakfast (eating from noon to 8pm) is the most common 16:8 implementation.

Yes — water, black coffee, and plain tea have minimal/no calories and do not break the fast. Some people allow small amounts of cream in coffee (debated). Anything with calories, artificial sweeteners (in large amounts), or insulin-spiking ingredients technically breaks a metabolic fast. Hydration is important during fasting.

IF works primarily by reducing total calorie intake — you have fewer hours to eat. Research shows IF produces weight loss similar to continuous calorie restriction when total calories are matched. The advantage: many people find it easier to skip a meal than to count calories throughout the day. It is a schedule, not a magic fix.

Pregnant or breastfeeding women, people with a history of eating disorders, those with type 1 diabetes or on insulin medication, children and adolescents, anyone who is underweight, and people with certain medical conditions. Always consult a doctor before starting, especially if you have any metabolic conditions or take medications.