What Is a Calorie Calculator?
A calorie calculator estimates the number of calories your body needs each day to maintain, lose, or gain weight. It uses established scientific formulas to compute your Basal Metabolic Rate (BMR) — the energy your body burns at rest — and then adjusts it based on your physical activity level to produce your Total Daily Energy Expenditure (TDEE).
This calculator uses the Mifflin-St Jeor equation, which was published in 1990 and is widely regarded as the most accurate predictive equation for estimating BMR in healthy adults. The American Dietetic Association recommends the Mifflin-St Jeor equation as the best starting point for estimating calorie needs.
How the Mifflin-St Jeor Equation Works
The Mifflin-St Jeor equation calculates BMR using four variables: weight, height, age, and gender.
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
TDEE = BMR × Activity Multiplier
The equation accounts for the fact that heavier and taller people have more tissue that requires energy, younger people have higher metabolic rates, and men typically have more lean muscle mass than women (which is why their constant is +5 instead of −161).
Understanding BMR vs TDEE
BMR (Basal Metabolic Rate) is the number of calories your body would burn if you did absolutely nothing all day — no movement, no digestion, no mental effort. It represents the energy needed purely for involuntary functions: heartbeat, breathing, cell repair, temperature regulation, and organ function. BMR typically accounts for 60-75% of your total daily calories.
TDEE (Total Daily Energy Expenditure) is your real-world calorie burn, which includes BMR plus three additional components:
- Physical activity: Exercise and daily movement (15-30% of TDEE)
- Thermic effect of food (TEF): Energy used to digest food (~10% of TDEE)
- Non-exercise activity thermogenesis (NEAT): Fidgeting, walking, standing (varies widely)
Your TDEE is the number that matters for weight management. Eat below your TDEE to lose weight, at your TDEE to maintain, and above your TDEE to gain weight.
Activity Level Multipliers Explained
| Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, no exercise. Mostly sitting throughout the day. |
| Lightly Active | 1.375 | Light exercise 1-3 days/week. Walks, light jogging, yoga. |
| Moderately Active | 1.55 | Moderate exercise 3-5 days/week. Gym sessions, running, swimming. |
| Very Active | 1.725 | Hard exercise 6-7 days/week. Sports training, intensive gym workouts. |
| Extra Active | 1.9 | Very hard exercise plus physical job. Athletes, construction workers, military training. |
How to Use Calorie Calculations for Weight Goals
Once you know your TDEE, managing your weight becomes a matter of energy balance:
For Weight Loss
Create a calorie deficit by eating fewer calories than your TDEE. A deficit of 500 calories per day leads to approximately 0.5 kg (1 pound) of weight loss per week. A deficit of 250 calories per day yields 0.25 kg per week — slower but more sustainable and easier to maintain. Never go below 1,200 calories/day (women) or 1,500 calories/day (men) without medical supervision.
For Weight Maintenance
Eat at your TDEE. In practice, your weight will fluctuate by 1-2 kg due to water retention, food volume, and other factors. Aim for a stable trend over weeks, not day-to-day precision.
For Weight Gain
Eat a calorie surplus above your TDEE. A surplus of 250-500 calories per day supports lean muscle gain when combined with strength training. Larger surpluses lead to faster weight gain but with a higher proportion of fat.
Disclaimer: This calculator provides estimates based on general population formulas. Individual results vary based on genetics, body composition, medical conditions, and medications. Always consult a healthcare professional or registered dietitian before making significant changes to your diet.
Frequently Asked Questions
What is the most accurate calorie calculator formula?
The Mifflin-St Jeor equation, used in this calculator, is considered the most accurate formula for estimating BMR in the general population. A 2005 review in the Journal of the American Dietetic Association compared several formulas and found that Mifflin-St Jeor predicted measured resting metabolic rate within 10% in more non-obese and obese individuals than other equations. It replaced the older Harris-Benedict equation (1919) as the recommended standard.
How many calories should I eat to lose weight?
Subtract 500 calories from your TDEE for a weight loss rate of approximately 0.5 kg (1 pound) per week. For a gentler approach, subtract 250 calories for 0.25 kg per week. The "right" deficit depends on how much weight you need to lose, your starting point, and what is sustainable for your lifestyle. Crash diets with extreme deficits (1,000+ calories below TDEE) are not recommended as they can lead to muscle loss, nutrient deficiencies, and metabolic adaptation.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy your body uses at complete rest for vital functions — heartbeat, breathing, cell production. TDEE (Total Daily Energy Expenditure) is your total calorie burn including BMR, physical activity, digestion, and non-exercise movement. For a moderately active person, TDEE is typically 1.55 times their BMR.
How accurate is this calorie calculator?
The Mifflin-St Jeor equation predicts BMR within about 10% for most healthy adults. Factors that can reduce accuracy include very high or low body fat percentage, certain medical conditions (thyroid disorders, PCOS), medications, and extreme ages. Treat the result as a starting point, track your weight for 2-4 weeks, and adjust intake by 100-200 calories if results differ from expectations.
Should I eat back exercise calories?
It depends on how you set your activity level. If you selected "Moderately Active" and you exercise 3-5 days per week, your TDEE already includes those exercise calories — do not eat them back or you will double-count. If you use "Sedentary" as your base and track exercise separately, you can eat back 50-75% of estimated exercise calories (fitness trackers tend to overestimate by 20-50%).
Why do men and women have different calorie needs?
On average, men have more lean muscle mass and less body fat than women of the same height and weight. Muscle tissue is metabolically active (burns calories at rest), while fat tissue is relatively inert. This biological difference means men typically have a higher BMR. The Mifflin-St Jeor equation accounts for this with a +5 constant for men and -161 for women.