Whether your goal is losing weight, building muscle, or simply maintaining your current physique, everything starts with knowing how many calories your body actually needs each day. This number is not a universal constant — it depends on your size, age, sex, and how active you are. The process involves two calculations: first your Basal Metabolic Rate (BMR), then your Total Daily Energy Expenditure (TDEE). Here is how to do both.
Step 1: Gather Your Measurements
Every calorie estimation formula requires four inputs:
- Weight — in kilograms. To convert from pounds, divide by 2.205 (e.g., 175 lb = 79.4 kg).
- Height — in centimeters. To convert from inches, multiply by 2.54 (e.g., 70 in = 177.8 cm).
- Age — in years. BMR declines with age, roughly 1–2% per decade after age 20.
- Biological sex — men and women have different coefficients in all major BMR equations due to differences in average lean mass and hormonal profiles.
For the most accurate results, weigh yourself first thing in the morning after using the bathroom and before eating or drinking. Measure height without shoes.
Step 2: Calculate Your BMR
Your Basal Metabolic Rate is the number of calories your body burns at complete rest — just to keep your organs functioning, your blood circulating, and your cells regenerating. It typically accounts for 60–75% of total daily calorie burn.
The Mifflin-St Jeor equation, published in 1990, is considered the most accurate for most adults and is the formula recommended by the Academy of Nutrition and Dietetics:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5 Example: A 30-year-old man, 80 kg, 180 cm: BMR = 800 + 1,125 − 150 + 5 = 1,780 cal/day.
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161 Example: A 28-year-old woman, 65 kg, 165 cm: BMR = 650 + 1,031 − 140 − 161 = 1,380 cal/day.
Other commonly used formulas include the Harris-Benedict equation (1919, revised 1984) and the Katch-McArdle formula, which uses lean body mass instead of total weight and is preferred by people who know their body fat percentage. You can compare all four formulas side by side with the BMR Calculator.
Step 3: Apply Your Activity Multiplier for TDEE
BMR only tells you what your body burns at rest. To get your Total Daily Energy Expenditure (TDEE) — the actual number of calories you burn in a typical day — multiply your BMR by an activity factor:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly Active | 1.375 | Light exercise 1–3 days per week |
| Moderately Active | 1.55 | Moderate exercise 3–5 days per week |
| Very Active | 1.725 | Hard exercise 6–7 days per week |
| Extremely Active | 1.9 | Physical job plus intense training |
Using the 30-year-old man from our example (BMR = 1,780) who exercises moderately 4 days per week: TDEE = 1,780 × 1.55 = 2,759 calories per day. This is his maintenance level — eating this amount should keep his weight stable over time.
Get your exact TDEE with our precision calculator
Try the TDEE Calculator →Step 4: Adjust for Your Goal
Weight Loss
To lose weight, you need to eat fewer calories than your TDEE. A deficit of 500 calories per day produces approximately 1 pound of fat loss per week (since 1 pound of body fat contains roughly 3,500 calories). Most nutrition professionals recommend a moderate deficit of 300–500 calories to preserve muscle mass and avoid metabolic slowdown.
For our example: 2,759 − 500 = 2,259 calories per day for steady weight loss of about 1 lb/week. Plan your deficit timeline with the Calorie Deficit Calculator.
Muscle Gain
Building muscle requires a calorie surplus — eating more than your TDEE. A surplus of 250–500 calories per day supports muscle growth while minimizing unnecessary fat gain. Combined with progressive resistance training and adequate protein (1.6–2.2 g per kg of bodyweight), this surplus provides the energy your body needs to synthesize new muscle tissue.
Maintenance
Eating at your TDEE keeps your weight stable. This is the right target if you are happy with your current body composition and want to fuel your activity without gaining or losing. Even at maintenance, the composition of your diet matters — adequate protein, fiber, and micronutrients support health regardless of calorie goals.
Common Mistakes to Avoid
- Overestimating activity level. Most people are less active than they think. If you exercise 3 times a week but spend the rest of the day at a desk, "lightly active" is usually more accurate than "moderately active."
- Ignoring adaptive thermogenesis. As you lose weight, your BMR decreases because there is less body mass to maintain. Recalculate every 10–15 pounds lost.
- Setting too aggressive a deficit. Deficits larger than 750 calories per day increase muscle loss, slow metabolism, and are harder to sustain. Consistency with a moderate deficit outperforms crash dieting every time.
- Treating the number as exact. All BMR formulas produce estimates with a margin of error around 5–10%. Use the calculation as a starting point, then adjust based on real-world results over 2–3 weeks.
Key Takeaways
- BMR is your baseline — the calories your body burns at rest, accounting for 60–75% of daily expenditure.
- TDEE = BMR × activity factor gives you the total calories you actually burn each day.
- Subtract 300–500 cal for weight loss, add 250–500 cal for muscle gain, or eat at TDEE for maintenance.
- Recalculate as your body changes. Every 10–15 pounds of weight change warrants a fresh calculation.