Calorie & TDEE Calculator
Find out how many calories you burn each day and how many you need to maintain, lose, or gain weight. Uses the Mifflin-St Jeor equation, recommended by the Academy of Nutrition and Dietetics.
Reviewed by Richard Ross · Last updated April 2026
How Calorie & TDEE Calculator works
BMR — Basal Metabolic Rate
BMR is the number of calories your body burns at complete rest to maintain basic functions — breathing, circulation, cell production, and temperature regulation. It accounts for roughly 60–75% of total daily calorie expenditure. The Mifflin-St Jeor equation (1990) is the most widely recommended formula for estimating BMR, more accurate than the older Harris-Benedict equation for most people.
TDEE — Total Daily Energy Expenditure
TDEE is your total calorie burn over a day, accounting for physical activity. It is calculated by multiplying BMR by an activity factor: sedentary (1.2), lightly active (1.375), moderately active (1.55), very active (1.725), and extra active (1.9). These multipliers are approximate — individual metabolism varies, and "activity level" is inherently imprecise.
Weight change and calorie balance
One kilogram of body fat stores approximately 7,700 kilocalories of energy. A daily deficit of 550 kcal (half a kilogram of fat per week) or a surplus of 550 kcal should theoretically produce the corresponding weight change. In practice, the body adapts to sustained deficits through reduced metabolic rate and changes in activity, making actual weight loss slower than the arithmetic suggests over longer periods.
Limitations
These figures are estimates. Individual BMR can vary by up to 20% from the formula prediction due to genetics, hormones, lean muscle mass, and health conditions. People with thyroid disorders, insulin resistance, or polycystic ovary syndrome may find their actual needs differ significantly. For weight management beyond general guidance, a registered dietitian can provide personalised assessment.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR is the calories you burn if you lay still all day — your body's minimum energy requirement to keep functioning. TDEE adds the calories burned through activity (exercise, walking, daily movement). TDEE is the number you compare against food intake to determine whether you're in a calorie surplus, deficit, or balance.
How accurate is the Mifflin-St Jeor equation?
The Mifflin-St Jeor equation predicts BMR within about 10% for most adults. It is more accurate than the Harris-Benedict equation for most body types. Highly muscular people will have higher actual BMRs than predicted (muscle burns more calories than fat), and very sedentary people may have lower actual TDEEs than the multipliers suggest.
How many calories should I eat to lose weight?
A modest deficit of 300–500 kcal per day typically produces 0.3–0.5 kg of weight loss per week without feeling overly restricted. Deficits larger than 1,000 kcal per day are generally not recommended for unsupervised weight loss as they risk muscle loss and nutritional deficiencies. The NHS recommends a target of no less than 1,200 kcal/day for women and 1,500 kcal/day for men.
Do I need to count calories to lose weight?
Not necessarily. Many people achieve sustainable weight loss by changing food quality, portion awareness, and eating habits without tracking every calorie. Calorie counting is a tool that works well for some people and poorly for others. The most effective approach is one you can sustain long-term.
What is BMR and how does it relate to daily calorie needs?
Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic functions at complete rest — breathing, circulation, cell repair, and temperature regulation. It accounts for 60-70% of total daily energy expenditure. Your Total Daily Energy Expenditure (TDEE) is BMR multiplied by an activity factor (1.2 for sedentary to 1.9 for very active). Most calorie calculators estimate TDEE and then adjust for your goal.
How accurate are online calorie calculators?
Calorie calculators based on formulas like Mifflin-St Jeor or Harris-Benedict give a population-average estimate. Individual variation in metabolic rate can be 10-15% above or below the formula prediction due to genetics, hormones, gut microbiome, and other factors. Treat calculated calorie needs as a starting point and adjust based on real-world results over 2-4 weeks. Tracking body weight trends is more reliable than trusting a single calculated figure.
What is the difference between calories and kilocalories?
In everyday language, "calorie" and "kilocalorie" (kcal) are used interchangeably for food energy. A food label showing "200 calories" means 200 kilocalories. The scientific calorie (lowercase, small c) is 1/1000th of a kilocalorie and is not used in nutrition. In the UK, food labels typically show energy in both kcal and kilojoules (kJ), with 1 kcal ≈ 4.184 kJ. When counting calories from food labels, use the kcal figure.
How does sleep affect calorie balance?
Poor sleep disrupts hunger-regulating hormones: ghrelin (which stimulates appetite) rises and leptin (which signals fullness) falls with sleep deprivation. Sleep-deprived people consume an average of 385 additional calories per day, according to a King's College London meta-analysis. Sleep also reduces physical performance, making it harder to maintain an exercise routine. Getting 7-9 hours consistently is an often-overlooked component of weight management.
Do calories from different macronutrients matter equally?
All calories contribute to energy balance, but macronutrients differ in how they affect satiety, thermogenesis, and hormones. Protein has the highest thermic effect (20-30% of its calories are burned in digestion), is the most satiating macronutrient, and preserves muscle during a calorie deficit. Fat is the least satiating per calorie but is essential for hormone production. Carbohydrates are the primary fuel for high-intensity exercise. For weight management, total calories matter most, but protein intake affects body composition.
What is the minimum safe calorie intake?
NHS guidance advises against diets below 1,000 kcal/day for women or 1,200 kcal/day for men without medical supervision, as these can lead to nutritional deficiencies, muscle loss, metabolic adaptation, and gallstones. Very low calorie diets (VLCDs) of 800 kcal/day or less are sometimes used medically for rapid weight loss in people with obesity but require clinical monitoring. Severe restriction also often leads to rebound weight gain when normal eating resumes.
This calculator provides estimates for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.