Basal Metabolic Rate (BMR)
BMR is the number of calories your body burns at complete rest to maintain basic functions — breathing, circulation, cell repair, temperature regulation. It's the minimum your body needs if you did nothing all day.
Two common formulas:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
- Men: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)
- Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)
For a 30-year-old woman, 165 cm, 68 kg: BMR ≈ 1,474 kcal/day.
Total Daily Energy Expenditure (TDEE)
BMR is how much you'd burn in a coma. TDEE is how much you actually burn accounting for your activity level. TDEE = BMR × activity multiplier:
- **Sedentary** (desk job, little exercise): × 1.2
- **Lightly active** (light exercise 1–3 days/week): × 1.375
- **Moderately active** (moderate exercise 3–5 days/week): × 1.55
- **Very active** (hard exercise 6–7 days/week): × 1.725
- **Extra active** (physical job + hard exercise): × 1.9
The same woman with a moderately active lifestyle: 1,474 × 1.55 ≈ 2,285 kcal/day TDEE.
This is your maintenance level — eating this much, you stay the same weight.
The Calorie Deficit
To lose weight, consume fewer calories than TDEE. The standard guidance:
**1 kg of body fat ≈ 7,700 kcal.** To lose 0.5 kg/week, you need a 550 kcal/day deficit. To lose 1 kg/week, 1,100 kcal/day.
A deficit of 500–750 kcal/day is sustainable for most people and produces 0.5–0.75 kg of weight loss per week. Larger deficits cause muscle loss, fatigue, and metabolic adaptation (your body slows down to compensate).
For our example: 2,285 − 600 = 1,685 kcal/day target for ~0.55 kg/week loss.
Protein Target
Protein is the most important macro when in a deficit. It preserves muscle mass while losing fat. Higher protein also increases satiety and has a higher thermic effect (your body burns ~25% of protein calories just digesting it).
Target: **1.6–2.2 g of protein per kg of body weight** (higher end if you're active or lifting weights). Our example woman at 68 kg: 109–150 g protein/day = 436–600 kcal from protein.
Fat: Minimum Required
Fat is essential for hormone production, vitamin absorption, and cell function. The minimum is 0.5–1 g per kg of bodyweight. Going below this impairs hormone function. For most people, allocating 25–35% of calories to fat is sensible.
Carbohydrates: The Remainder
Carbohydrates fill the remaining calorie budget. They're not essential in the way protein and fat are, but they fuel exercise performance and are the brain's preferred fuel. Low-carb diets work for weight loss, but they're not inherently superior to balanced diets at the same calorie level.
Carbs at 4 kcal/g, protein at 4 kcal/g, fat at 9 kcal/g.
The Numbers Aren't Perfect
Calorie calculators are estimates. Activity multipliers are approximations. Food labels have ±20% accuracy. The thermodynamics are real, but the precise numbers aren't. Track intake and weight for 2–3 weeks, then adjust the target based on actual results rather than treating the initial calculation as gospel.
Weight also fluctuates by 1–3 kg day to day based on water retention, food volume, and glycogen. A weekly average is more informative than daily weigh-ins.
NoxaKit's Calorie Deficit Calculator, BMR Calculator, and Macro Nutrient Splitter handle all of this in the browser — no account, no data upload.