When should I choose Katch-McArdle over Mifflin-St Jeor?

Use Katch-McArdle whenever you have an accurate measurement of body fat percentage from DEXA or hydrostatic weighing. Because adipose tissue burns only ~4.5 kcal/kg/day while skeletal muscle burns ~13 kcal/kg/day and organs burn ~200-400 kcal/kg/day, basing calculations on Lean Body Mass eliminates weight-bias errors.

How much does age reduce BMR every decade?

BMR declines by approximately 1% to 2% per decade after age 25-30. Most of this decline is not biological aging per se, but sarcopenia—the gradual loss of metabolically active skeletal muscle mass and reduction in spontaneous physical activity (NEAT).

Can resistance training permanently elevate my BMR?

Yes. Gaining 5 kg (11 lbs) of lean skeletal muscle increases resting metabolic rate by approximately 65-100 kcal per day directly, and significantly more when factoring in post-exercise metabolic remodeling and glycogen replenishment.

When should I choose Katch-McArdle over Mifflin-St Jeor?

Use Katch-McArdle whenever you have an accurate measurement of body fat percentage from DEXA or hydrostatic weighing. Because adipose tissue burns only ~4.5 kcal/kg/day while skeletal muscle burns ~13 kcal/kg/day and organs burn ~200-400 kcal/kg/day, basing calculations on Lean Body Mass eliminates weight-bias errors.

How much does age reduce BMR every decade?

BMR declines by approximately 1% to 2% per decade after age 25-30. Most of this decline is not biological aging per se, but sarcopenia—the gradual loss of metabolically active skeletal muscle mass and reduction in spontaneous physical activity (NEAT).

Can resistance training permanently elevate my BMR?

Yes. Gaining 5 kg (11 lbs) of lean skeletal muscle increases resting metabolic rate by approximately 65-100 kcal per day directly, and significantly more when factoring in post-exercise metabolic remodeling and glycogen replenishment.

ZenFit Tools/metabolism/Basal Metabolic Rate (BMR) Comparative Calculator

5 min readClinical Comparison

Basal Metabolic Rate (BMR) Comparative Calculator

Name: Basal Metabolic Rate (BMR) Comparative Calculator
Author: ZenFit Tools

Side-by-side comparative analysis of Mifflin-St Jeor, Revised Harris-Benedict, Katch-McArdle, and Schofield WHO equations.

Formula: Comparative matrix across 4 clinical BMR prediction methodologies

Input Parameters

Metric

Biological Sex

Age30 yrs

Body Weight78 kg

Height178 cm

Body Fat Percentage (Optional / Estimate)15%

Instant Biometric Computation

Multi-Formula Comparative Mean BMR

1788 kcal/day

Max formula variance: 70 kcal

Mifflin-St Jeor1748 kcal

Revised Harris-Benedict1817 kcal

Schofield (WHO)1784 kcal

Katch-McArdle (LBM)1802 kcal

Export to Fitness Logs & Spreadsheets

Save this calculation for your training log: Apple Notes, Notion, Obsidian, Google Sheets, or Excel.

In-Browser Computation

How This Calculator Works & Mathematical Formula

Mifflin-St Jeor (1990): 10W + 6.25H - 5A (+5 for men, -161 for women)
Revised Harris-Benedict (1984): Men: 88.362 + 13.397W + 4.799H - 5.677A | Women: 447.593 + 9.247W + 3.098H - 4.330A
Katch-McArdle (1983): 370 + 21.6 × LBM (kg)
Schofield / Oxford WHO (1985): Age-stratified regression constants based on total body weight

Standard Physiological Guidelines & Scientific References

Clinical Society Guidelines

Frankenfield D, et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789.
Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182.
Schofield WN. Predicting basal metabolic rate, new standards and review of previous work. Hum Nutr Clin Nutr. 1985;39 Suppl 1:5-41.

Peer-Reviewed Citations

Frankenfield D, et al. J Am Diet Assoc. 2005.
Mifflin MD, et al. Am J Clin Nutr. 1990.

Formula Limitations, Safety Guidance & Doctor Consultation

Formula Limitations & Population Assumptions

•BMR accounts for approximately 60% to 75% of total daily caloric burn. It does not include calories burned walking, digesting food, or exercising.

•Severe caloric restriction (<1,000 kcal/day) causes down-regulation of thyroid hormone T3 and up-regulation of reverse T3 (rT3), depressing BMR below predicted formulas.

When to Consult a Physician

Always consult a licensed medical professional before implementing significant changes to your caloric intake, fasting routine, hydration targets, or strenuous exercise programming. Seek immediate medical evaluation if you experience unexplained chest discomfort, irregular heartbeats, shortness of breath, dizziness, syncope, or if you have pre-existing cardiovascular, metabolic, renal, or endocrine conditions.

Educational Scope

Not medically reviewed. The results and estimates generated by this calculator are derived strictly from published population formulas and sports science research. They are intended for general athletic education and personal informational purposes only, and must never be construed as clinical diagnosis, medical prescription, or specialized healthcare advice.

Frequently Asked Questions (4 Technical Inquiries)

The original 1919 Harris-Benedict study examined young, lean, physically active college students and laboratory staff in cold environments. Subsequent re-evaluations (Roza & Shizgal 1984) and modern studies show it overestimates modern sedentary adults’ BMR by approximately 5% to 15%.

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