Which BMR formula is most accurate?

The Mifflin-St Jeor equation (1990) is considered the most accurate for most non-obese adults, validated against indirect calorimetry. The Harris-Benedict equation (revised 1984) is older but widely used. The Katch-McArdle formula is most accurate when lean body mass is known, making it ideal for athletes.

What is TDEE and how is it different from BMR?

TDEE (Total Daily Energy Expenditure) is your total caloric need including all daily activity. It is calculated by multiplying BMR by an activity factor: sedentary (×1.2), lightly active (×1.375), moderately active (×1.55), very active (×1.725), or extremely active (×1.9). TDEE is the number of calories you need to consume to maintain your current weight.

BMR & TDEE Calculator – Basal Metabolic Rate & Daily Calorie Needs

Q: What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic physiological functions at complete rest — including breathing, circulation, cell production, and temperature regulation. It represents approximately 60–70% of total daily energy expenditure in sedentary individuals.

What Is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate is the minimum number of calories your body requires to sustain essential physiological functions at complete rest — breathing, heartbeat, cell repair, temperature regulation, and organ function. BMR accounts for approximately 60–70% of total daily energy expenditure in sedentary individuals and decreases with age as lean muscle mass naturally declines.

The Three BMR Formulas

Formula	Year	Best For	Error Range
Mifflin-St Jeor	1990	Most non-obese adults	±10%
Harris-Benedict (revised)	1984	General population	±12%
Katch-McArdle	1996	Athletes with known lean mass	±5% (when BF% known)

Activity Multipliers (Harris-Benedict)

Level	Multiplier	Description
Sedentary	× 1.2	Desk job, minimal movement
Lightly Active	× 1.375	Light exercise 1–3 days/week
Moderately Active	× 1.55	Exercise 3–5 days/week
Very Active	× 1.725	Hard exercise 6–7 days/week
Extremely Active	× 1.9	Physical job + daily training

Macronutrient Distribution

The macronutrient targets shown are based on the general guidelines of the Dietary Reference Intakes (DRI): protein 20–25%, carbohydrates 45–50%, fat 25–35% of total calories. These are general starting points — individual needs vary significantly by goal, medical condition, and dietary preference.

Frequently Asked Questions

What is the difference between BMR and TDEE?+

BMR is the calories burned at complete rest — if you did nothing but lie in bed all day. TDEE (Total Daily Energy Expenditure) adds the energy cost of all daily activity, exercise, and the thermic effect of food. TDEE is the number you actually need to consume to maintain your weight. Eating below TDEE causes weight loss; eating above causes gain.

Why does my BMR decrease with age?+

BMR decreases with age primarily because of the gradual loss of lean muscle mass (sarcopenia) that begins in the third decade of life. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. Additionally, hormonal changes (declining testosterone, growth hormone, and thyroid function) contribute to reduced resting metabolism. Resistance training can partially offset age-related BMR decline.

How many calories should I eat to lose 1 kg per week?+

One kilogram of fat contains approximately 7,700 kcal. To lose 1 kg per week, you would need a daily calorie deficit of approximately 1,100 kcal (7,700 ÷ 7). Most guidelines recommend a maximum deficit of 500–750 kcal/day (0.5 kg/week) for sustainable, safe weight loss. Larger deficits risk muscle loss, nutrient deficiencies, and metabolic adaptation. Always consult a dietitian for personalised advice.

Is Katch-McArdle more accurate than Mifflin-St Jeor?+

For athletes and individuals with known body fat percentage, yes — Katch-McArdle can be more accurate because it calculates BMR from lean body mass directly, bypassing the height/weight/age approximation. However, if body fat percentage is estimated (not measured), the error introduced negates the formula's advantage. For most people without DEXA or caliper measurements, Mifflin-St Jeor remains the recommended choice.

Related Tools

Use BMR alongside Caloric Needs Calculator for detailed macronutrient planning, BMI Calculator for weight classification, and Body Fat Percentage for lean mass estimation to use with Katch-McArdle.

References

Mifflin MD, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990;51(2):241-247.
Harris JA, Benedict FG. A Biometric Study of Human Basal Metabolism. Carnegie Institution, 1919. (Revised Roza & Shizgal, 1984.)
Katch V, McArdle W. Nutrition, Weight Control, and Exercise. 3rd ed. Lea & Febiger, 1988.
Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. NAP, 2005.

⚠️ Medical Disclaimer: BMR and TDEE estimates have an inherent margin of error of ±10–20%. These are general reference values. For clinical nutrition support, medical weight management, or eating disorder recovery, always work with a registered dietitian or physician.