This science-based calculator estimates potential fat loss during intermittent fasting based on your body composition, fasting duration, and metabolic factors. Input your details to estimate weight and fat loss during different fasting protocols.
Medical Disclaimer: This tool provides general educational estimates. Consult a licensed medical provider before starting any fasting program.
Your Basal Metabolic Rate (BMR): calories/day
Your Total Daily Energy Expenditure (TDEE): calories/day
Estimated weight loss during fasting period:
Estimated fat loss during fasting period:
Estimated water weight loss during fasting period:
This calculator estimates how much fat you may lose while following intermittent fasting protocols based on your body composition and fasting frequency.
Estimates are based on clinical fasting research and average fat loss rates over time. Weekly changes are modeled by fasting intensity and consistency.
For weekly fat loss charts, protocol breakdowns, and expert strategy: Full guide coming soon
Want to see detailed weekly fasting weight loss charts and estimates based on different protocols? Our complete fasting weight loss timeline shows you exactly what to expect week-by-week with different fasting schedules. View Fasting Weight Loss Timeline →
Most people see initial water weight loss within 24-48 hours of starting intermittent fasting. More significant fat loss typically begins after 2-3 weeks of consistent fasting, with visible results often appearing after 4-8 weeks. Consistency is key for long-term results.
Some muscle loss is possible during extended fasting periods, but it's minimal when fasting is done correctly. To preserve muscle mass, maintain adequate protein intake during eating windows (1.6-2.2g per kg of body weight) and incorporate resistance training into your routine 2-3 times per week.
The most effective schedule is one you can maintain consistently. Many find success with 16:8 fasting (16 hours fasting, 8 hours eating) as it's sustainable. For more aggressive results, some prefer 20:4 or alternate day fasting, though these may be harder to maintain long-term.
Yes, exercise during fasting can enhance fat burning. Low to moderate intensity activities like walking, yoga, or light resistance training are well-tolerated during fasted states. For high-intensity training, consider scheduling workouts near the end of your fasting period or during your eating window for optimal performance.
Intermittent fasting is not recommended for pregnant or breastfeeding women, people with eating disorders, type 1 diabetics, or those with certain medical conditions. Children, adolescents, and elderly individuals should approach fasting cautiously. Always consult a healthcare provider before starting any fasting regimen.