Health & Medicine · Dietetics & Metabolism
Calorie Deficit Calculator
Calculate your daily calorie deficit based on your TDEE and weight-loss goal to determine how much you need to eat to lose fat at a controlled rate.
Calculator
Formula
TDEE (Total Daily Energy Expenditure) is the total calories your body burns per day. Target Intake is your planned daily calorie consumption. A deficit of 3,500 kcal corresponds to approximately 1 lb (0.45 kg) of fat loss. Weekly Loss is expressed in pounds.
Source: Hall, K.D. et al. (2012). Quantification of the effect of energy imbalance on bodyweight. The Lancet, 378(9793), 826–837.
How it works
Step 1 — Estimating BMR with Mifflin–St Jeor: Your Basal Metabolic Rate is the number of calories your body requires just to maintain vital functions at complete rest — breathing, circulation, cellular repair, and thermoregulation. The Mifflin–St Jeor equation, validated in a landmark 1990 study by Mifflin et al. in the American Journal of Clinical Nutrition, calculates BMR as: For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5; For women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) − 161. This equation is consistently cited as the most accurate predictive equation for healthy adults and has largely replaced the older Harris–Benedict formula in clinical settings.
Step 2 — Scaling to TDEE with an Activity Multiplier: Because you are not lying still all day, your BMR must be multiplied by a Physical Activity Level (PAL) factor to account for the calories burned through daily movement, exercise, and the thermic effect of food. The multipliers used here (1.2 to 1.9) are drawn from FAO/WHO/UNU energy requirement guidelines. A sedentary office worker uses a factor of 1.2, while someone with a physically demanding job or who trains twice daily uses 1.9. The result is your TDEE — the total number of calories you need each day just to maintain your current weight.
Step 3 — Calculating the Deficit: To lose fat, you must consume fewer calories than your TDEE — this creates a negative energy balance, forcing the body to draw on stored fat for fuel. The widely-used approximation is that 1 kilogram of body fat stores approximately 7,700 kcal of energy (or 3,500 kcal per pound). Therefore, to lose 0.5 kg per week, you need a daily deficit of (0.5 × 7,700) ÷ 7 ≈ 550 kcal. Your Target Daily Intake is simply TDEE minus this daily deficit. Most dietitians recommend keeping intake above 1,200 kcal/day for women and 1,500 kcal/day for men to preserve muscle mass and micronutrient adequacy.
Worked example
Example: 35-year-old male, 85 kg, 180 cm, moderately active, targeting 0.5 kg/week loss.
Step 1 — BMR: BMR = (10 × 85) + (6.25 × 180) − (5 × 35) + 5 = 850 + 1,125 − 175 + 5 = 1,805 kcal/day
Step 2 — TDEE: Moderately active multiplier = 1.55. TDEE = 1,805 × 1.55 = 2,798 kcal/day (rounded to 2,798).
Step 3 — Daily Deficit Required: To lose 0.5 kg/week: (0.5 kg × 7,700 kcal/kg) ÷ 7 days = 550 kcal/day deficit.
Step 4 — Target Intake: 2,798 − 550 = 2,248 kcal/day.
Result: This individual should consume approximately 2,248 kcal per day to lose roughly 0.5 kg (1.1 lbs) of fat per week. At this rate, losing 5 kg would take approximately 10 weeks. This is considered a moderate, sustainable deficit well within clinical guidelines.
Limitations & notes
The Mifflin–St Jeor equation is a population-level estimate and may over- or underestimate true TDEE by ±10–15% for any given individual due to variations in muscle mass, hormonal status, gut microbiome, and metabolic adaptation. The 7,700 kcal/kg fat rule is also a simplification — real weight loss includes water and lean tissue changes, especially in the early weeks. People with thyroid disorders, insulin resistance, or those who have previously lost significant weight (adaptive thermogenesis) may see actual results diverge from predictions. This calculator does not constitute medical or nutritional advice; individuals with health conditions should consult a registered dietitian or physician before making significant dietary changes. Very low calorie intakes (below 1,200 kcal for women or 1,500 kcal for men) can be unsafe without medical supervision.
Frequently asked questions
What is a safe calorie deficit for fat loss?
Most nutritional guidelines and clinical practice recommend a deficit of 500–750 kcal/day, corresponding to approximately 0.5–0.75 kg (1–1.5 lbs) of fat loss per week. Larger deficits (above 1,000 kcal/day) increase the risk of muscle loss, nutrient deficiencies, fatigue, and metabolic adaptation, where your body lowers its TDEE in response to undereating. A moderate, consistent deficit is almost always more effective long-term than an aggressive short-term cut.
Why is the Mifflin–St Jeor equation used instead of Harris–Benedict?
The Mifflin–St Jeor equation was developed in 1990 using a more modern, diverse population dataset compared to the original 1919 Harris–Benedict study. Multiple validation studies, including a 2005 comparison by Frankenfield et al. in the Journal of the American Dietetic Association, found Mifflin–St Jeor to be the most accurate predictive equation for resting metabolic rate in healthy adults, with roughly 70% of predictions falling within 10% of measured values. It is now the preferred equation recommended by the Academy of Nutrition and Dietetics.
Does my calorie intake need to change as I lose weight?
Yes — as your body weight decreases, your BMR and TDEE also decrease, meaning the same absolute calorie intake will produce a smaller deficit over time. This is one reason weight loss often slows or plateaus after the first few weeks. It is good practice to recalculate your TDEE every 4–6 weeks or for every 3–5 kg of weight lost, and adjust your target intake accordingly to continue progressing toward your goal.
What is the difference between a calorie deficit for fat loss vs. weight loss?
Total body weight includes fat mass, muscle mass, bone, water, and organ tissue. When you create a calorie deficit, the body draws on multiple energy stores — primarily fat but also some muscle glycogen and, without adequate protein intake and resistance training, lean muscle tissue. True fat loss is best achieved by combining a moderate calorie deficit with sufficient dietary protein (1.6–2.2 g/kg body weight) and resistance exercise, which helps preserve muscle mass and ensure the weight lost comes predominantly from fat stores.
How accurate is the 7,700 kcal per kg of fat rule?
The figure of approximately 7,700 kcal per kilogram (or 3,500 kcal per pound) of adipose tissue is a biochemical approximation based on the energy density of triglycerides stored in fat cells, accounting for the fact that adipose tissue is roughly 87% lipid and 13% water and protein. While this is a useful rule of thumb, actual weight loss is more complex — early rapid weight loss is often partly water and glycogen, and metabolic adaptation can reduce the actual deficit below what is calculated. For practical planning purposes, however, the 7,700 kcal/kg approximation remains widely accepted by dietitians and researchers.
Last updated: 2025-01-15 · Formula verified against primary sources.