The Minimum Calories You Should Eat Without Losing Muscle
Slashing calories too aggressively while dieting tends to burn through muscle along with fat, which lowers your basal metabolic rate (BMR) and makes rebound weight gain more likely once the diet ends. Your BMR is the minimum energy your body needs just to breathe, pump blood, and maintain temperature with zero activity. This calculator uses the Mifflin-St Jeor equation to calculate your BMR from sex, age, height, and weight.
Generally, even while dieting, it's not recommended to eat below your BMR, and a common safety floor is at least 1,200 kcal/day for women and 1,500 kcal/day for men. This calculator shows whichever is higher - your calculated BMR or the sex-based floor - as your "minimum safe intake." Staying above this limit while increasing calorie burn through activity and exercise is the safer path to losing fat without losing muscle.
Extreme low-calorie diets can produce fast-looking weight loss in the short term, but most of that loss is water and muscle, and it's rarely sustainable. For lasting results, stay above your calculated minimum, eat enough protein, and shift more of your training toward strength work rather than cardio alone.
Frequently Asked Questions
Your BMR is the minimum energy your body needs just to breathe, pump blood, and stay warm. Eating below it forces your body to break down muscle for energy, which lowers your metabolism and makes rebound weight gain more likely.
A short period may not cause major harm, but sustained intake below this limit raises the risk of nutrient deficiency, muscle loss, and hormonal imbalance. Staying below it long-term without medical supervision isn't recommended.