Question 1

What is Basal Metabolic Rate (BMR)?

Accepted Answer

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to sustain essential physiological functions — heartbeat, respiration, brain activity, organ function, and thermoregulation. BMR accounts for approximately 60–70% of total daily energy expenditure (TDEE). It is measured under strict conditions (fasted, rested, thermoneutral) and is best estimated using validated predictive equations such as Mifflin-St Jeor (1990), Harris-Benedict Revised (1984), or Katch-McArdle (1996).

Question 2

Which BMR formula is most accurate?

Accepted Answer

The Mifflin-St Jeor equation (1990) is the current gold standard recommended by the Academy of Nutrition and Dietetics (AND) and ACSM for the general adult population. It predicts BMR within ±10% for most adults. The Harris-Benedict Revised (Roza & Shizgal 1984) is used in WHO/clinical-research contexts and has similar accuracy. The Katch-McArdle formula (1996) is the most accurate for individuals with known body fat percentage — particularly athletes — because it uses lean body mass directly and bypasses the overestimation that can occur in Harris-Benedict with high-BMI individuals.

Question 3

What is TDEE and how is it calculated?

Accepted Answer

Total Daily Energy Expenditure (TDEE) is the total calories burned per day, including all activity. It is calculated as BMR × Physical Activity Level (PAL) multiplier, following WHO/FAO/UNU 2004 guidelines. PAL multipliers range from 1.2 (sedentary — desk job, little/no exercise) to 1.9 (extra active — physical job plus daily training). Eating at TDEE maintains current weight; a consistent deficit below TDEE produces fat loss; a surplus above TDEE produces weight gain.

Question 4

How many calories should I eat to lose weight?

Accepted Answer

Safe, evidence-based fat loss targets a deficit of 300–750 kcal/day below TDEE, producing 0.25–0.5 kg of fat loss per week. A 500 kcal/day deficit yields approximately 0.5 kg/week (1 kg fat ≈ 7,700 kcal). Deficits exceeding 1,000 kcal/day accelerate lean mass loss and are not recommended without medical supervision. The Calorie Goal Planner mode in this calculator sets targets for Aggressive Loss (−1 kg/week), Moderate Loss (−0.5 kg/week), Maintenance, Lean Gain (+0.25 kg/week), and Bulk (+0.5 kg/week).

Question 5

What are the recommended macros for fat loss or muscle gain?

Accepted Answer

The ACSM-2016 evidence-based macro split for body composition goals is 30% protein / 40% carbohydrates / 30% fat. Protein should be prioritised at ≥1.6–2.2 g/kg body weight per day (higher end during fat loss to preserve lean mass). During a fat-loss phase, increasing protein to 35–40% of calories and moderating carbohydrates is widely supported by meta-analyses. For muscle building, adequate carbohydrates (40–50%) support training performance and glycogen replenishment.

Question 6

How does BMR change with age?

Accepted Answer

BMR declines approximately 1–2% per decade from age 30, primarily due to sarcopenia (age-related loss of lean muscle mass). The average BMR for a 30-year-old 70 kg male is approximately 1,840 kcal/day; by age 70+ it falls to approximately 1,560 kcal/day — a difference of ~280 kcal/day. Each 1 kg of muscle gained increases BMR by approximately 13 kcal/day. Resistance training 2–3 times per week is the most evidence-backed intervention for preserving BMR with age.

Question 7

Can I use lbs and inches instead of kg and cm?

Accepted Answer

Yes. This BMR calculator includes a Metric/Imperial unit toggle. When you switch to Imperial, all measurement fields (weight, height) convert automatically from kg/cm to lbs/in. The calculations always use metric values internally (Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas are defined in SI units), so results are identical regardless of which unit system you select.

Type	Description
Mifflin-St Jeor	Most accurate for most people
Harris-Benedict	Revised Harris-Benedict equation
Katch-McArdle	Uses lean body mass

Type	Description
Mifflin-St Jeor	Most accurate for most people
Harris-Benedict	Revised Harris-Benedict equation
Katch-McArdle	Uses lean body mass

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