INTERMITTENT FASTING
CALCULATOR
Calculate your fasting and eating windows, and get a personalized IF schedule.
Your IF Plan
Your IF Schedule
🆋 Eating Window--
🚫 Fasting Window--
⏱ Last Meal By--
⏱ Break Fast At--
Calories (eating days)--
Calories (fast days if 5:2)--
Advertisement
Ad space — paste AdSense code here
Intermittent Fasting Protocols
Related Articles
What Is Intermittent Fasting?
Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. Unlike traditional diets, IF focuses on when you eat rather than what you eat. The most common protocols are 16:8 (16 hours fasting, 8-hour eating window), 18:6, 20:4, 5:2 (normal eating 5 days, 500–600 calories 2 days), and OMAD (one meal per day). IF works primarily by reducing calorie intake through the shortened eating window.
RM
Built by Ren Martin
Sports coach · 20+ years in fitness · Used this calculator personally
Frequently Asked Questions
Does intermittent fasting work for weight loss?
Yes. Meta-analyses consistently show IF produces comparable or slightly better weight loss versus continuous caloric restriction over 6–24 weeks. The mechanism is primarily calorie reduction through the compressed eating window. IF may also provide additional metabolic benefits including improved insulin sensitivity, though research is ongoing.
Does intermittent fasting slow metabolism?
Short-term fasting (under 72 hours) does not meaningfully slow metabolism and may actually slightly increase it through elevated norepinephrine. The metabolic slowdown associated with dieting comes from sustained caloric restriction and weight loss, not from the fasting pattern itself. What matters for fat loss is the total calorie deficit over time, not when those calories are consumed.
Can I exercise while fasting?
Yes, and many people train effectively in a fasted state. Research shows no significant difference in fat loss or muscle retention between fasted and fed training when total protein and calorie intake are matched across the day. If you find fasted training reduces performance significantly, training near the end of your fasting window — just before your eating window opens — is a practical compromise.
Can I drink water during the fasting window?
Yes. Water, black coffee, and plain tea contain negligible calories and do not break a fast in a metabolic sense. Avoid anything with calories or insulin-stimulating ingredients (cream, sugar, sweeteners in some research) during the fasting window.