Calculate your intermittent fasting eating window, calorie targets, and expected weight loss. Free IF calculator for 16:8, 18:6, and 5:2. No signup.
Intermittent fasting works by reducing the window in which you eat — making it easier to eat fewer calories without obsessive tracking. The 16:8 method (16 hours fasting, 8 hours eating) is the most popular and sustainable. Our calculator finds your personal eating window, daily calorie target within that window, and projected weekly weight loss.
16:8 (most popular): Fast 16 hours, eat between noon and 8pm for example. Sustainable long-term, minimal social disruption. 18:6: Fast 18 hours, eat between 1pm and 7pm. More aggressive calorie reduction for faster results. 5:2: Eat normally 5 days, restrict to 500-600 calories on 2 non-consecutive days. Good for those who prefer unrestricted days over daily windows. OMAD (one meal a day): 23:1 — very aggressive, difficult to sustain.
Allowed during fasting window without breaking the fast: Water (unlimited), Black coffee (no milk, cream, or sugar), Plain unsweetened tea, Sparkling water. Breaks the fast and ends fasting benefits: Any food including small amounts, Milk or cream in coffee, Fruit juice or smoothies, Sweetened beverages even if zero calorie (debated). The goal is keeping insulin low during the fasting window.
Yes — multiple studies show IF produces similar weight loss to continuous calorie restriction. The advantage is simplicity: fewer decisions about what to eat, natural reduction in calorie intake within a shorter window, and for many people easier adherence than daily calorie counting. Results depend on not overeating during the eating window.
IF has no rules about what to eat — only when. However food quality still matters for health and results. During your eating window prioritize: high protein to preserve muscle, vegetables and fruits for micronutrients, whole grains over refined carbs, healthy fats. Overeating junk food in 8 hours defeats the calorie reduction goal.
IF is not recommended for: pregnant or breastfeeding women, people with history of eating disorders, type 1 diabetics on insulin without medical supervision, children and teenagers, and those who are underweight. People with type 2 diabetes should consult their doctor first as IF can significantly impact blood sugar medications.
Yes — every FreeFixo tool, including the Intermittent Fasting Calculator — Find Your Eating Window and Calorie Goal, is 100% free with no paywall, no premium tier, and no usage limits. You do not need to create an account, enter a credit card, or share an email.
The Intermittent Fasting Calculator — Find Your Eating Window and Calorie Goal uses the same formulas, rates, and reference data that financial planners, professionals, and government sources publish. Results are estimates intended for planning and education — for situations involving large sums or legal consequences, confirm with a qualified professional before acting.
No signup is ever required. The Intermittent Fasting Calculator — Find Your Eating Window and Calorie Goal runs entirely in your browser — your inputs are never sent to a server, and we do not store, track, or share your data. Open it, get your answer, close the tab.