Health & Fitness Calculators

How health metrics work together: BMI, BMR, and TDEE

Health numbers are most useful as a chain, not in isolation. Start with BMI, which screens weight relative to height: a 70 kg adult who is 175 cm tall has a BMI of 70 / (1.75 × 1.75) = 22.9, squarely in the 18.5–24.9 healthy range. BMI does not distinguish muscle from fat, so pair it with body-fat and ideal-weight estimates — two people with the same 22.9 BMI can look and perform very differently if one lifts weights and the other does not.

Next, estimate burn. BMR is what that same 70 kg adult burns at complete rest — roughly 1,600–1,700 kcal per day for a 30-year-old man using the Mifflin-St Jeor equation — while TDEE multiplies BMR by activity: sedentary (×1.2) gives about 2,000 kcal, moderately active (×1.55) gives about 2,600 kcal, and very active (×1.9) exceeds 3,100 kcal. That 600–1,100 kcal swing explains why generic “eat 2,000 calories” advice fails: the right target depends on your size, age, and training load.

Finally, turn TDEE into a plan. Subtract 300–500 kcal per day for sustainable fat loss of about 0.25–0.5 kg per week, or add 200–300 kcal for lean muscle gain, then split calories into macros: around 1.6–2.2 g of protein per kg of body weight (112–154 g for our 70 kg example), 45–65% of calories from carbohydrates for active people, and the rest from fats. Check water intake (about 30–35 ml per kg, or 2.1–2.5 liters), sleep consistency, and heart-rate zones alongside the scale — if weight stalls for 2–3 weeks, recalculate TDEE first, because a 5 kg loss alone can lower daily burn by 100–150 kcal. Re-measure monthly and adjust portions before cutting further, since sleep debt and stress can mask steady fat-loss progress.