Knowing how many calories you burn in a day is the foundation of any realistic eating plan — whether you want to lose fat, gain muscle, or simply maintain your weight. This calorie needs calculator estimates your two most important energy numbers: your Basal Metabolic Rate (BMR), the calories your body burns at rest just to keep you alive, and your Total Daily Energy Expenditure (TDEE), the calories you actually burn after adding movement. It uses the Mifflin-St Jeor equation, the resting-energy formula most nutrition researchers consider the most accurate for healthy adults.
Adjust any input and every figure on the result card updates instantly, including the daily calorie targets for mild weight loss and mild weight gain.
How to Use
- Enter your Weight in kilograms. If you know your weight in pounds, divide by 2.205 first (for example, 154 lb ≈ 70 kg).
- Enter your Height in centimeters. A 5 ft 9 in person is about 175 cm; multiply inches by 2.54 if you need to convert.
- Enter your Age in completed years. Resting metabolism trends downward roughly 1–2% per decade after adulthood, so age matters.
- Choose your Biological Sex. The Mifflin-St Jeor equation adds +5 for men and subtracts 161 for women, reflecting typical differences in lean mass.
- Pick your Activity Level honestly — this is the step most people get wrong. "Moderately active" (1.55) means regular exercise or a physically demanding job several days a week, not simply walking to the car.
- Read the result card. Maintenance Calories (TDEE) is the number that keeps your weight stable. To lose weight, eat below it; to gain weight, eat above it.
The card also shows BMR (the floor your body needs to function), a mild weight-loss target of about 500 kcal/day below maintenance, and a mild weight-gain target of about 500 kcal/day above maintenance.
The Mifflin-St Jeor Equation
Your resting metabolic rate is estimated with the Mifflin-St Jeor equation published in 1990:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) − 161
You then multiply BMR by an activity factor to reach TDEE:
| Activity level | Factor | Who it describes |
|---|---|---|
| Sedentary | 1.2 | Desk job, little intentional exercise |
| Lightly active | 1.375 | Light exercise 1–3 days/week |
| Moderately active | 1.55 | Moderate exercise 3–5 days/week |
| Very active | 1.725 | Hard exercise 6–7 days/week |
| Extra active | 1.9 | Physical job or twice-daily training |
For a 70 kg, 175 cm, 30-year-old man, BMR works out to roughly 1,649 kcal/day. At a moderate activity factor of 1.55, his maintenance calories are about 2,556 kcal/day. Eating 500 less (≈2,056 kcal/day) trends toward losing about 0.45 kg, or one pound, per week; eating 500 more trends toward gradual weight gain.
A common mistake is over-estimating activity by a full factor. Choosing "very active" when you are really "moderately active" can inflate TDEE by 300–400 kcal/day — enough to quietly erase a planned deficit. Be conservative, then adjust after two weeks of scale readings.
Examples
Example 1 — Maintenance for a moderately active man. A 30-year-old man weighing 70 kg at 175 cm, exercising 3–5 days a week, gets a BMR near 1,649 and a TDEE of about 2,556 kcal/day. That is the number that keeps him at the same weight; roughly 40% of those calories could come from carbs, 30% from protein, and 30% from fats if he prefers a balanced plate.
Example 2 — A woman aiming to lose fat. A 35-year-old woman, 60 kg and 165 cm, with a sedentary desk job (1.2 factor). Her BMR is about 1,320 kcal/day and her maintenance is roughly 1,584 kcal/day. A safe starting target is maintenance minus 500, or about 1,084 kcal/day, never below her BMR for long without supervision.
Example 3 — Weight gain for hard training. A 25-year-old man, 80 kg and 180 cm, who trains twice daily (1.725 factor). His BMR is near 1,768 kcal/day and his TDEE about 3,050 kcal/day. Adding a modest 500 gives him a ~3,550 kcal/day surplus to support lean mass gain rather than only fat.
FAQ
How many calories do I need a day?
It depends on your weight, height, age, sex, and activity level. This calculator estimates your maintenance calories (TDEE) directly from those inputs. As a rough rule, most sedentary adult women fall near 1,600–2,000 kcal/day and most sedentary adult men near 2,000–2,600 kcal/day, but your personalized number is what matters.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy you burn at complete rest to breathe, circulate blood, and maintain temperature. TDEE (Total Daily Energy Expenditure) multiplies BMR by your activity factor, so it includes walking, exercise, and daily movement. TDEE is always higher than BMR and is the number you use for meal planning.
How many calories should I eat to lose weight?
Start with your maintenance calories, then subtract about 500 kcal per day to target roughly 0.45 kg (1 lb) of weight loss per week. Avoid dropping far below your BMR for extended periods, because very low intakes reduce muscle mass, energy, and adherence. Re-evaluate after two weeks and adjust by a few hundred calories based on the scale.
How many calories should I eat to gain weight?
Add about 300–500 kcal per day above your maintenance calories. A modest surplus builds mostly lean mass when paired with resistance training; a large surplus adds mostly fat. Aim for roughly 0.25 kg of gain per week rather than rapid weight gain.
Why is the Mifflin-St Jeor equation used?
Published in 1990, the Mifflin-St Jeor equation predicts resting metabolism more accurately than older formulas such as Harris-Benedict across a wide range of body types in healthy adults. It remains the default in most modern nutrition and fitness calculators.
Why does my activity level choice change the result so much?
Activity multipliers range from 1.2 to 1.9, a difference of more than 50%. Choosing the right factor is therefore as important as your weight or height. Most people who train a few days a week are best described as "moderately active" (1.55); reserve "very active" and "extra active" for daily hard training or physical labor.
Disclaimer
This calorie needs calculator is provided for informational purposes only and is not medical advice. Estimates are based on the Mifflin-St Jeor equation and the inputs you enter, and individual energy needs vary with body composition, genetics, medications, thyroid function, and health conditions. The results are not a diagnosis, treatment plan, or recommendation. If you are pregnant, breastfeeding, managing diabetes or another medical condition, or have a history of disordered eating, consult a registered dietitian or qualified healthcare provider before changing your diet.