Calorie Deficit Calculator

A calorie deficit occurs when you consume fewer calories than your body burns in a day. Your body requires a certain number of calories to maintain all its functions — this is your Total Daily Energy Expenditure (TDEE). When you eat less than your TDEE, your body draws on stored energy (primarily body fat) to make up the difference. Consistently sustaining a deficit of approximately 3,500 calories results in roughly one pound of fat loss. For example, a 500-calorie daily deficit creates about 3,500 calories of deficit per week, projecting to approximately one pound of weight loss per week. The relationship isn't perfectly linear for every person, but it's a reliable planning framework.

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — essentially the energy needed to keep your heart beating, lungs breathing, and organs functioning. This calculator uses the Mifflin-St Jeor equation, which is widely considered the most accurate BMR formula for most adults. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor that accounts for the calories you burn through movement, exercise, and daily activity. Your TDEE is your true maintenance calorie level — eat less than this to lose weight, more to gain. Most people underestimate their TDEE because they forget to account for even light daily movement.

Most health authorities, including the CDC and NHS, recommend a daily deficit of 500–750 calories, which projects to roughly 1–1.5 pounds of weight loss per week. This rate is generally considered sustainable and preserves muscle mass better than aggressive cuts. Deficits larger than 1,000 calories per day (targeting more than 2 lbs/week) increase the risk of muscle loss, nutritional deficiencies, fatigue, and metabolic adaptation. Women are generally advised not to go below 1,200 calories per day, and men not below 1,500 calories per day, unless under direct medical supervision. Slower, consistent weight loss tends to be more maintainable long-term.

Several factors can cause real-world weight loss to differ from projections. Water retention fluctuates significantly day to day due to sodium intake, hormones, carbohydrate stores, and inflammation. Metabolic adaptation — where your body reduces its calorie burn in response to a prolonged deficit — means TDEE decreases as you lose weight. This calculator uses your current weight for all calculations; as you lose weight, your TDEE drops, making the same calorie intake produce a smaller deficit over time. Additionally, the 3,500 calories-per-pound rule is an approximation. Body composition changes (losing fat but gaining muscle through exercise) can also make the scale misleading. Weigh yourself consistently in the same conditions and track trends over weeks, not days.

Yes. Exercise increases your TDEE, which means you burn more calories and can achieve a larger deficit without cutting more food. When you select your activity level in this calculator, it already accounts for your regular exercise routine — a sedentary multiplier of 1.2 versus a very active multiplier of 1.9 can differ by hundreds of calories per day. However, people often overestimate calorie burn from exercise, so it's better to be conservative with your activity level selection unless your exercise is genuinely consistent. Many people find success with a combined approach: a moderate dietary deficit plus regular resistance training to preserve muscle mass during weight loss.

Weight loss simply refers to a decrease on the scale, which can come from water loss, muscle loss, or fat loss. Fat loss specifically refers to the reduction of adipose tissue, which is what most people want when they say 'weight loss.' Rapid calorie deficits tend to cause a higher proportion of muscle loss alongside fat loss. To maximize fat loss while preserving muscle, most fitness professionals recommend pairing a moderate calorie deficit (500–750 calories/day) with adequate protein intake (0.7–1 gram per pound of body weight) and resistance exercise. This approach is slower on the scale but produces better body composition results. A BMI or scale weight alone doesn't capture these important distinctions.