Calorie Calculator
Calculate your daily calorie needs based on age, gender, weight, height, and activity level. Uses the Mifflin-St Jeor equation for accurate BMR and TDEE estimation.
Key features
- Mifflin-St Jeor BMR calculation
- Five activity level options
- Deficit and surplus recommendations
- Gender-specific calculations
Guide
Calorie calculation is the process of estimating how much energy your body needs each day to maintain, lose, or gain weight. Your body burns calories continuously to power basic biological functions like breathing, circulation, cell repair, and temperature regulation. Physical activity, digestion, and exercise add to this baseline expenditure. Understanding your daily calorie needs is the foundation of any nutrition plan, whether your goal is fat loss, muscle gain, or maintaining your current body composition. This guide covers the science behind calorie calculations, the formulas used, and how to apply the numbers to real-world eating habits. A calorie (technically a kilocalorie, abbreviated kcal) is a unit of energy. One calorie is the energy needed to raise the temperature of one kilogram of water by one degree Celsius. When food labels say a serving contains 200 calories, they mean that burning that food in a calorimeter releases enough energy to raise 200 kg of water by one degree. Your body extracts this energy through metabolic processes rather than combustion, but the energy content is the same. The international unit is the kilojoule (kJ), where 1 kcal equals 4.184 kJ. Most nutrition resources use calories (kcal), and this guide follows that convention. Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a 24-hour period. TDEE consists of three components. Basal Metabolic Rate (BMR) accounts for 60 to 75 percent of TDEE and represents the energy needed to keep your body alive at complete rest. The Thermic Effect of Food (TEF) accounts for about 10 percent and represents the energy used to digest, absorb, and process the food you eat. Physical activity, including both structured exercise and non-exercise activity (walking, fidgeting, standing), accounts for the remaining 15 to 30 percent. Basal Metabolic Rate is calculated using formulas that take your weight, height, age, and sex as inputs. The most widely used formula is the Mifflin-St Jeor equation, published in 1990. For men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5. For women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161. Research has shown that Mifflin-St Jeor is the most accurate predictive equation for healthy adults, estimating actual measured BMR within 10 percent for the majority of people. The Harris-Benedict equation is an older formula still commonly used. Originally published in 1919 and revised in 1984, it tends to overestimate calorie needs slightly compared to Mifflin-St Jeor. The revised Harris-Benedict equation for men is: BMR = (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age) + 88.362. For women: BMR = (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age) + 447.593. The WebRecast calculator uses Mifflin-St Jeor as its default formula due to its higher accuracy in validation studies. The Katch-McArdle formula is more accurate for athletic individuals because it uses lean body mass (total weight minus fat mass) instead of total body weight. The formula is BMR = 370 + (21.6 x lean body mass in kg). This approach accounts for the fact that muscle tissue burns more calories at rest than fat tissue. If two people weigh the same but one has 15 percent body fat and the other has 30 percent, the leaner person has a higher BMR. The limitation is that you need to know your body fat percentage to use this formula, which requires separate measurement. The Cunningham equation is another lean-mass-based formula: BMR = 500 + (22 x lean body mass in kg). It tends to produce slightly higher estimates than Katch-McArdle and is sometimes preferred for athletes with high muscle mass. The difference between Katch-McArdle and Cunningham is small (typically less than 100 calories) and both outperform weight-based formulas for people at the extremes of body composition, either very lean or carrying significant excess fat. Activity multipliers convert BMR to TDEE by accounting for your daily movement. The standard multipliers are: sedentary (little or no exercise) = BMR x 1.2, lightly active (light exercise 1 to 3 days per week) = BMR x 1.375, moderately active (moderate exercise 3 to 5 days per week) = BMR x 1.55, very active (hard exercise 6 to 7 days per week) = BMR x 1.725, and extremely active (very hard exercise plus a physical job or training twice per day) = BMR x 1.9. These multipliers are estimates. Most people overestimate their activity level. If you work a desk job and exercise for 30 minutes three times per week, you are likely lightly active, not moderately active. The activity multiplier system has known limitations. It bundles all forms of physical activity into a single number. Two people who are both "moderately active" might have very different TDEE if one has a physically demanding job and the other sits all day but trains hard for an hour. More precise approaches use MET (Metabolic Equivalent of Task) values to calculate the calorie cost of each activity separately. Walking at 3 mph is approximately 3.5 METs. Running at 6 mph is about 10 METs. Sitting at a desk is 1.3 METs. Multiplying METs by body weight in kg and hours spent gives calories burned per activity. Summing all activities produces a more accurate TDEE. To lose weight, you need to eat fewer calories than your TDEE, creating a calorie deficit. A deficit of approximately 500 calories per day produces roughly 0.45 kg (1 pound) of fat loss per week, since one pound of body fat contains approximately 3,500 calories of stored energy. A deficit of 250 calories per day produces about half a pound of loss per week. Larger deficits produce faster loss but increase the risk of muscle loss, nutrient deficiencies, metabolic adaptation, and adherence failure. A moderate deficit of 300 to 500 calories below TDEE is sustainable for most people. The 3,500-calorie rule (1 pound of fat = 3,500 calories) is a simplification. In reality, the calorie cost of weight loss changes as you lose weight. Your BMR decreases because you have less body mass to support. Metabolic adaptation further reduces expenditure. Your body also does not exclusively burn fat during a deficit. Some energy comes from muscle breakdown, glycogen depletion, and water loss, especially in the early weeks. Dynamic models like the NIH Body Weight Planner account for these adaptations and provide more accurate predictions of weight loss timelines. To gain weight, primarily as muscle, you need a calorie surplus combined with resistance training. A surplus of 250 to 500 calories per day supports muscle growth without excessive fat gain. The rate of muscle gain depends on training experience: beginners can gain 0.5 to 1 kg of muscle per month with proper training and nutrition. Intermediate lifters gain about half that rate, and advanced lifters gain even less. Eating a large surplus does not accelerate muscle growth beyond a point. It just increases fat gain. Macronutrient distribution matters alongside total calories. The three macronutrients are protein (4 calories per gram), carbohydrates (4 calories per gram), and fat (9 calories per gram). Alcohol provides 7 calories per gram but is not classified as a macronutrient. Protein is the most important macronutrient for body composition. Research consistently supports consuming 1.6 to 2.2 grams of protein per kilogram of body weight per day for people who exercise regularly. Protein supports muscle repair and growth, increases satiety, and has the highest thermic effect of food (20 to 30 percent of protein calories are used in digestion). Carbohydrates fuel high-intensity exercise and support brain function. The brain alone uses approximately 120 grams of glucose per day. Active individuals benefit from higher carbohydrate intake, typically 3 to 5 grams per kilogram of body weight for moderate exercise and up to 8 to 10 grams per kilogram for endurance athletes. Fat is essential for hormone production (including testosterone and estrogen), vitamin absorption (vitamins A, D, E, K are fat-soluble), and cell membrane integrity. A minimum of 0.5 to 0.7 grams of fat per kilogram of body weight is necessary for hormonal health, with most recommendations falling between 20 to 35 percent of total calories. Metabolic adaptation is a real phenomenon where your BMR decreases during a calorie deficit beyond what the weight loss alone would explain. Your body becomes more efficient, reducing non-essential energy expenditure. You fidget less, move less spontaneously, and your body temperature may drop slightly. Thyroid hormone levels (particularly T3) decrease. The sympathetic nervous system becomes less active. This adaptation can slow weight loss progress even when you are accurately tracking calories. The practical response is to take periodic diet breaks (eating at maintenance for one to two weeks) and to avoid extreme calorie deficits that accelerate adaptation. Non-exercise activity thermogenesis (NEAT) is the energy burned through all daily movements that are not structured exercise: walking, standing, typing, cooking, fidgeting, maintaining posture. NEAT varies enormously between individuals and can account for 200 to 900 calories per day. Studies by Dr. James Levine at the Mayo Clinic found that NEAT is the most variable component of TDEE and is the primary factor separating people who gain weight easily from those who do not. People who are naturally active (take stairs, walk during phone calls, stand at their desk) burn significantly more through NEAT than those who sit most of the day. Age affects calorie needs because BMR decreases by approximately 1 to 2 percent per decade after the age of 20. This decline is partly due to loss of lean muscle mass (sarcopenia) and partly due to hormonal changes. A 50-year-old has a lower BMR than a 25-year-old of the same weight, height, and sex. Resistance training slows this decline by preserving muscle mass, which is why strength training becomes increasingly important with age. The average adult gains about 0.5 to 1 kg of fat per year while losing muscle, a gradual shift that compounds over decades. Sex differences in calorie needs exist because men typically have more lean mass and less body fat than women at the same body weight. The Mifflin-St Jeor equation accounts for this with different constants (the +5 for men versus -161 for women reflects approximately a 166-calorie difference at the same weight, height, and age). Hormonal differences also play a role: testosterone promotes muscle mass (and thus higher BMR), while estrogen promotes fat storage. Women's calorie needs also fluctuate throughout the menstrual cycle, with a slight increase during the luteal phase (about 100 to 300 extra calories per day in some studies). Calorie tracking methods vary in accuracy. Food scales are the most accurate, weighing food in grams and looking up calorie values in a database. Measuring cups and spoons are less accurate but better than visual estimation, which typically underestimates portions by 30 to 50 percent. Calorie tracking apps (MyFitnessPal, Cronometer, MacroFactor) provide large food databases and barcode scanning. Nutrition labels on packaged foods are allowed a 20 percent margin of error by FDA regulations, which means a food labeled at 200 calories could contain up to 240. Restaurant meals are even less predictable, with studies showing actual calories can exceed stated values by 10 to 50 percent. The accuracy of any calorie calculator depends on the accuracy of your inputs. Most people underestimate their food intake by 20 to 40 percent when self-reporting. They also overestimate their activity level. These two biases compound to produce an inflated expectation of weight loss. If you calculate a 500-calorie deficit but actually eat 200 more calories than you track and burn 100 fewer through activity, your real deficit is only 200 calories. Honest, precise tracking for at least two to four weeks gives you an accurate baseline. Calorie calculations are starting points, not absolute numbers. Individual variation in metabolic rate, gut microbiome, food absorption, and activity efficiency means that two people with identical stats on paper can have different actual calorie needs. Use the calculated number as a starting point. Track your weight over two to three weeks (weighing daily and using a weekly average to smooth out water weight fluctuations). If your weight is stable, the calculated TDEE is close to your actual expenditure. If you are gaining, your actual TDEE is lower. If you are losing, it is higher. Adjust your intake based on real-world results rather than clinging to a calculated number. The WebRecast calorie calculator takes your weight, height, age, sex, and activity level as inputs. It calculates your BMR using Mifflin-St Jeor, applies the appropriate activity multiplier to estimate TDEE, and shows calorie targets for weight loss, maintenance, and weight gain. The calculator also suggests macronutrient breakdowns for each goal. Use the output as your starting target and adjust based on how your body responds over the following weeks. Common mistakes in calorie management include: setting too aggressive a deficit and burning out within weeks, not accounting for liquid calories (coffee drinks, juice, alcohol, which can easily add 300 to 500 untracked calories per day), forgetting cooking oils and condiments (a tablespoon of olive oil adds 120 calories), eating back exercise calories as estimated by fitness trackers (which overestimate burn by 20 to 90 percent), and not being consistent long enough to evaluate results. Fat loss and muscle gain are slow processes. Give any calorie target at least three to four weeks before concluding it is not working. Meal timing and frequency have less impact on body composition than total daily calorie and macronutrient intake, but some practical guidelines apply. Protein distribution across the day matters: consuming 20 to 40 grams of protein per meal across 3 to 5 meals provides a more consistent stimulus for muscle protein synthesis than consuming your entire protein intake in one or two meals. Pre-workout nutrition (eating 1 to 3 hours before training) ensures adequate energy for performance. Post-workout nutrition (within 2 hours after training) supports recovery, though the anabolic window is wider than the 30-minute myth suggests. Calorie cycling is a strategy where you eat more on training days and less on rest days. The simplest approach adds 200 to 300 calories on training days (primarily from carbohydrates to fuel workouts) and subtracts the same amount on rest days. Over a week, the average daily intake remains the same as a flat approach. Some people find calorie cycling easier to follow psychologically because higher-calorie training days feel less restrictive. The physiological benefits are modest but include better workout performance on higher days and potentially enhanced fat oxidation on lower days. Special populations have different calorie needs. Pregnant women need an additional 340 calories per day in the second trimester and 452 in the third trimester (not eating for two). Breastfeeding women need approximately 400 to 500 extra calories per day. Adolescents need more calories per kilogram of body weight than adults due to growth demands. Older adults (65+) need fewer total calories but more protein per kilogram (1.0 to 1.2 g/kg minimum) to counteract sarcopenia. People recovering from surgery or illness have elevated calorie needs (up to 20 to 40 percent above normal) to support tissue repair and immune function. Periodization of calorie intake is an advanced strategy where you alternate between phases of cutting (deficit), maintenance, and bulking (surplus) throughout the year. This approach prevents prolonged metabolic adaptation, supports hormonal health, and aligns calorie intake with training goals. A common pattern for recreational lifters is 8 to 12 weeks of cutting followed by 4 to 8 weeks of maintenance, then 8 to 16 weeks of lean bulking. Each phase uses a different calorie target calculated from your current weight and activity level. Reverse dieting (gradually increasing calories from a deficit back to maintenance over several weeks) helps minimize fat regain during the transition.
Frequently asked questions
What is BMR?
Basal Metabolic Rate is the number of calories your body needs at complete rest to maintain basic functions like breathing and circulation.
How accurate is this calculator?
The Mifflin-St Jeor equation is considered the most accurate BMR formula, but individual metabolism can vary by 5-10%.
