Calorie Deficit Calculator

Understanding Calorie Deficit

A calorie deficit occurs when you consume fewer calories than your body burns. Your body compensates by using stored energy (primarily body fat) to meet its needs. One pound of body fat stores approximately 3,500 calories, so a daily deficit of 500 calories results in roughly 1 pound of weight loss per week. This calculator uses the Mifflin–St Jeor equation, widely regarded as the most accurate formula for estimating resting metabolic rate in healthy individuals.

Key Terms

• BMR (Basal Metabolic Rate) – The number of calories your body needs at complete rest to maintain basic functions such as breathing, circulation, and cell production.
• TDEE (Total Daily Energy Expenditure) – Your total calorie burn per day, calculated by multiplying BMR by an activity factor that accounts for exercise and daily movement.
• Calorie Deficit – The difference between your TDEE and your actual calorie intake. A consistent deficit leads to weight loss over time.

The Mifflin–St Jeor Equations

Activity Level Multipliers

Your TDEE is calculated by multiplying your BMR by an activity factor. Choose the level that best describes your typical week:

Safe Weight Loss Guidelines

Sustainable weight loss requires a moderate, consistent approach. Most health organizations recommend losing no more than 1–2 pounds (0.45–0.9 kg) per week. Rapid weight loss can lead to muscle loss, nutritional deficiencies, gallstones, and metabolic slowdown.

• Minimum intake: Women should generally not consume fewer than 1,200 calories per day, and men not fewer than 1,500 calories per day, without medical supervision.
• Protein intake: Aim for 0.7–1 g of protein per pound of body weight to preserve lean muscle mass during a deficit.
• Gradual approach: A deficit of 500–750 calories per day (1–1.5 lb/week) is considered safe and sustainable for most people.
• Monitor progress: Weigh yourself at the same time each day and track the weekly average to account for normal daily fluctuations.
• Consult a professional: If you have underlying health conditions, are pregnant or breastfeeding, or plan to lose more than 2 lb/week, seek guidance from a registered dietitian or physician.

Suggested Macronutrient Split During a Deficit

While total calories drive weight loss, macronutrient composition affects body composition, energy levels, and satiety. A common approach for preserving muscle during a calorie deficit is:

References

The formulas and guidelines used in this calculator are based on peer-reviewed research and recommendations from leading health organizations:

• Mifflin, M.D. et al. (1990) – A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), 241–247.
• National Heart, Lung, and Blood Institute (NHLBI) – Guide to Healthy Weight Loss
• World Health Organization (WHO) – Healthy Diet Fact Sheet
• Mayo Clinic – Counting Calories: Get Back to Weight-Loss Basics
• Frankenfield, D. et al. (2005) – Comparison of predictive equations for resting metabolic rate. Journal of the American Dietetic Association, 105(5), 775–789.

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