Calorie Deficit Calculator
How to Use This Tool
Enter your current weight, target weight, height, age, and biological sex. Select your typical activity level and choose between the Mifflin-St Jeor (recommended) or Harris-Benedict formula. Specify your weekly weight loss goal (0.25-2 kg or lbs). Optionally, check the box to see a macronutrient breakdown. Click Calculate to get your daily calorie target and estimated time to reach your goal. Use Reset to clear all fields and start over.
Formula and Logic
The calculator first determines your Basal Metabolic Rate (BMR)—the calories your body burns at complete rest—using one of two evidence-based equations:
- Mifflin-St Jeor (1990): Considered the most accurate for modern populations. For men: BMR = (10 Ă— weight in kg) + (6.25 Ă— height in cm) - (5 Ă— age) + 5. For women: BMR = (10 Ă— weight in kg) + (6.25 Ă— height in cm) - (5 Ă— age) - 161.
- Harris-Benedict (1984 revision): An older but still referenced formula. For men: BMR = (13.397 Ă— weight in kg) + (4.799 Ă— height in cm) - (5.677 Ă— age) + 88.362. For women: BMR = (9.247 Ă— weight in kg) + (3.098 Ă— height in cm) - (4.330 Ă— age) + 447.593.
Total Daily Energy Expenditure (TDEE) is BMR multiplied by an activity factor (1.2–1.9). The daily calorie target is TDEE minus the deficit needed for your weekly weight loss goal. The deficit is calculated as (weekly loss in kg × 7700 kcal) ÷ 7 days, based on the approximation that 1 kg of body fat contains about 7700 kcal. Time to target is (current weight - target weight) ÷ weekly loss goal.
Practical Notes
Individual metabolic rates vary significantly due to genetics, hormone levels, body composition, and medical conditions. This calculator provides estimates based on population averages; your actual needs may be 10–20% higher or lower. As you lose weight, your BMR decreases, so you’ll need to recalculate every 5–10 lbs (2.5–4.5 kg) lost to maintain your deficit. For best results, combine your calorie target with resistance training to preserve lean muscle mass and adequate protein intake (0.7–1g per pound of body weight). Rapid weight loss (more than 1% of body weight per week) often leads to muscle loss, metabolic slowdown, and rebound weight gain. Always consult with a healthcare provider or registered dietitian before starting any weight loss plan, especially if you have diabetes, thyroid issues, or other chronic conditions. This tool is not intended for pregnant or breastfeeding individuals, or for those with a history of eating disorders.
Why This Tool Is Useful
Understanding your precise calorie needs removes guesswork and helps you create a sustainable diet plan. By setting a realistic deficit, you can lose fat while maintaining energy for workouts and daily activities. The time-to-target estimate helps with goal-setting and motivation. The macronutrient breakdown ensures you’re consuming enough protein to support muscle retention during weight loss. This calculator is valuable for athletes preparing for competition, gym-goers during a cutting phase, and anyone seeking structured, science-based weight management.
Frequently Asked Questions
What if I don’t lose weight at the predicted rate?
Your actual weight loss may differ due to water retention, hormonal fluctuations, inaccurate food logging, or unaccounted calories (e.g., cooking oils, beverages). If you haven’t lost weight after 2–3 weeks of consistent adherence, reassess your portion sizes and consider recalculating with a lower activity level. You may also need to reduce calories by an additional 100–200 kcal/day or increase non-exercise activity (walking, standing).
Can I use this for weight gain or maintenance?
This calculator is designed for weight loss (calorie deficit). For weight gain, you’d need a calorie surplus—add 300–500 kcal to your TDEE. For maintenance, aim for your TDEE exactly. However, muscle gain during a surplus requires adequate protein and resistance training. Consider using a dedicated bulking calculator for more precise surplus recommendations.
How do I handle weight loss plateaus?
Plateaus are normal and often occur after 4–6 weeks as your body adapts. First, verify your calorie intake and portion accuracy. Then, try a “diet break” by eating at maintenance calories for 1–2 weeks to reset hormones before resuming your deficit. Alternatively, reduce calories by another 100–200 kcal, increase cardio volume, or incorporate refeeds (temporarily higher-carb days) to boost leptin. Ensure you’re getting 7–9 hours of sleep and managing stress, as these impact weight regulation.
Additional Guidance
Aim for a moderate deficit (500 kcal/day) to lose ~0.5 kg (1 lb) per week—this is sustainable for most people. Track your food intake using a verified app (e.g., MyFitnessPal, Cronometer) to stay within your target. Weigh yourself first thing in the morning, under consistent conditions, and use a 7-day average to account for daily fluctuations. Adjust your calories every 4–6 weeks or after every 5–10 lbs lost. Remember that body composition matters more than scale weight—focus on fat loss, not just weight loss, and consider measurements or progress photos. If you feel excessively fatigued, dizzy, or irritable, your deficit may be too aggressive; increase calories by 200–300 kcal. Finally, stay hydrated and prioritize whole foods over processed options to support overall health and satiety.