Calorie Calculator
Mifflin-St Jeor Equation
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161Maintenance Calories = BMR × Activity MultiplierWhat Are Calories?
A calorie is a unit of energy. In nutrition, when we say "calories" we actually mean kilocalories (kcal) — the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. Every process in your body, from breathing and circulating blood to thinking and exercising, requires calories as fuel.
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to maintain vital functions — heartbeat, breathing, cell repair, and temperature regulation. BMR typically accounts for 60–75% of total daily energy expenditure. It is influenced by age, sex, weight, height, and body composition; people with more muscle mass have higher BMRs.
Your Total Daily Energy Expenditure (TDEE), also called maintenance calories, is the total number of calories you burn in a day including physical activity. TDEE is calculated by multiplying BMR by an activity factor that reflects your lifestyle. Eating at your TDEE means your weight stays stable; eating above it leads to weight gain, and eating below it leads to weight loss.
Understanding your calorie needs is the foundation of any nutrition plan, whether your goal is losing fat, building muscle, or simply maintaining a healthy weight. This calculator uses the scientifically validated Mifflin-St Jeor equation to give you a personalised starting point that you can refine based on real-world results over time.
Mifflin-St Jeor Equation
The Mifflin-St Jeor equation was published in 1990 by Dr. Mark Mifflin and Dr. Sachiko St Jeor and has since become the gold standard for estimating BMR. A 2005 study by the American Dietetic Association compared several predictive equations and found that Mifflin-St Jeor was the most accurate, estimating measured resting metabolic rate within 10% for more subjects than any alternative formula.
The equation uses four variables: weight in kilograms, height in centimetres, age in years, and a sex-specific constant. For men, the formula is BMR = (10 × weight) + (6.25 × height) − (5 × age) + 5. For women, the constant changes to −161 instead of +5, reflecting the fact that women generally have a lower metabolic rate than men of the same size and age due to differences in body composition.
Once BMR is calculated, it is multiplied by an activity factor ranging from 1.2 (sedentary) to 1.9 (extra active) to estimate total daily calorie needs. This multiplier accounts for the thermic effect of food, non-exercise activity thermogenesis (NEAT), and deliberate physical exercise. Choosing the correct activity level is crucial — overestimating activity is the most common reason calorie targets don't produce expected results.
While the Mifflin-St Jeor equation is highly reliable for the general population, it may be less accurate for very muscular individuals, the very lean, or the very obese. In these cases, equations that account for lean body mass (such as Katch-McArdle) may be more appropriate. Nonetheless, for the vast majority of adults, Mifflin-St Jeor provides an excellent starting estimate.
Activity Level Guide
Selecting the right activity level is essential for an accurate calorie estimate. The activity multiplier transforms your BMR into your total daily energy expenditure. Below is a detailed breakdown of each level to help you choose the one that best matches your lifestyle.
| Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little to no exercise. Driving or commuting, mostly sitting throughout the day. |
| Lightly Active | 1.375 | Light exercise 1–3 days per week. Walking, casual cycling, or light housework. |
| Moderately Active | 1.55 | Moderate exercise 3–5 days per week. Jogging, swimming, gym workouts, active job. |
| Very Active | 1.725 | Hard exercise 6–7 days per week. Intense training, competitive sports, physically demanding work. |
| Extra Active | 1.9 | Very hard daily exercise plus a physical job. Professional athletes or military training. |
When in doubt, it is better to underestimate your activity level. Most people overestimate how active they are, which leads to eating more than they burn. Start with a conservative estimate, track your weight for 2–3 weeks, and adjust your activity level up if you are losing weight faster than intended.
Keep in mind that activity levels can change with the seasons, work schedules, and life events. Recalculating every few months ensures your calorie target remains aligned with your actual energy output.
Frequently Asked Questions
How many calories should I eat to lose weight?
To lose weight, you need to eat fewer calories than you burn (a calorie deficit). A deficit of 500 calories per day typically results in about 0.5 kg (1 lb) of weight loss per week. This calculator shows your maintenance calories and provides targets for mild, moderate, and extreme weight loss. A moderate deficit of 500 calories per day is generally recommended for sustainable, healthy weight loss.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body needs at complete rest — lying in bed all day doing nothing. TDEE (Total Daily Energy Expenditure) is your BMR plus all the calories you burn through daily movement, exercise, and digesting food. TDEE is the number you should use when planning your diet, because it reflects your actual daily calorie burn.
Is the Mifflin-St Jeor equation accurate?
The Mifflin-St Jeor equation is considered the most accurate BMR prediction formula for the general population. Studies show it estimates resting metabolic rate within 10% for most people. However, it is an estimate — individual metabolism can vary based on genetics, body composition, hormones, and other factors. Use the calculated number as a starting point, then adjust based on real-world results over 2–4 weeks.
Should I eat back the calories I burn from exercise?
It depends on your goal. If you are maintaining weight, eating back exercise calories keeps you at maintenance. If you are trying to lose weight, eating back all exercise calories will slow your progress. A common approach is to eat back about half of estimated exercise calories, since most trackers and machines tend to overestimate calories burned during workouts.
Why do men need more calories than women?
Men typically need more calories because they tend to have more muscle mass and less body fat than women of the same height and weight. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. This is reflected in the Mifflin-St Jeor equation, where the male formula includes a +5 constant while the female formula uses −161.
How to Use the Calorie Calculator
Using the Calorie Calculator is straightforward and designed for instant results. Simply input your required values into the designated fields above. The calculator will automatically process the inputs in real-time, applying the necessary mathematical formulas to provide an accurate, step-by-step breakdown (where applicable) instantly. If you input invalid data, clear error messages will guide you.
Formula & Methodology
This tool utilizes standard, universally accepted mathematical formulas to ensure 100% accuracy. Our methodology guarantees that edge cases—such as division by zero, negative roots, or complex numbers—are handled gracefully according to strict mathematical principles.
Common Examples
Whether you are a student verifying homework, a professional calculating technical specifications, or simply solving everyday math problems, this calculator eliminates manual errors. It replaces tedious handwritten calculations with instant, verifiable logic.
Frequently Asked Questions
Is the Calorie Calculator free to use?
Yes, this tool is 100% free, requires no registration, and contains zero intrusive ads.
How accurate are the results?
The calculations are performed using high-precision JavaScript mathematical libraries, ensuring accuracy up to 10 decimal places where applicable.