Basal metabolic rate (Mifflin-St Jeor) — weight & height in any unit.
**Male:** BMR = (10 × W) + (6.25 × H) − (5 × A) + 5 **Female:** BMR = (10 × W) + (6.25 × H) − (5 × A) − 161
The Mifflin-St Jeor equation (1990) calculates BMR in kilocalories per day based on weight, height, age, and biological sex. It is considered more accurate than the older Harris-Benedict equation, particularly for modern populations.
There are two versions — one for males and one for females:
BMR = (10 × 68) + (6.25 × 165) − (5 × 35) − 161 BMR = 680 + 1031.25 − 175 − 161 BMR = 1375.25
Result: BMR ≈ **1,375 kcal/day**
This result means the 35-year-old female in the example needs approximately 1,375 kilocalories per day just to keep her body alive at complete rest — no movement, no exercise, no digestion. This is her baseline energy requirement.
Remember: BMR is an estimate. Individual results can vary based on body composition, genetics, and health conditions.
Basal Metabolic Rate (BMR) represents about 60–75% of your total daily energy expenditure (TDEE). Even if you did nothing but lie still all day, your body would still burn a significant number of calories to maintain organ function, regulate temperature, produce hormones, and repair cells.
Published by Mifflin et al. in 1990 in the American Journal of Clinical Nutrition, the Mifflin-St Jeor equation was developed by measuring actual resting metabolic rates in a diverse sample of adults. Studies have shown it predicts BMR within 10% of measured values for most healthy adults — outperforming the older Harris-Benedict equation (1919) in accuracy.
| Term | Meaning | |---|---| | BMR | Calories burned at complete rest (no food, no movement) | | RMR | Resting Metabolic Rate — similar to BMR but measured under less strict conditions; slightly higher | | TDEE | Total Daily Energy Expenditure — BMR × activity factor; represents actual daily calorie needs |
To estimate total daily calorie needs, multiply your BMR by the appropriate factor:
First calculate your TDEE (BMR × activity factor). Then create a modest calorie deficit — typically 300–500 kcal/day below TDEE — to lose approximately 0.3–0.5 kg (0.5–1 lb) per week. Avoid going below your BMR value unless under medical supervision.
Both estimate BMR from weight, height, age, and sex. The Harris-Benedict equation was developed in 1919 and tends to overestimate BMR by about 5% in modern populations. The Mifflin-St Jeor equation (1990) was derived from a more contemporary sample and is considered more accurate for the average adult today.
BMR typically declines about 1–2% per decade after age 20, primarily due to age-related muscle loss (sarcopenia) and hormonal changes. Staying physically active and maintaining muscle mass through resistance exercise can slow this decline.
Essentially yes — BMR and resting caloric burn refer to the same concept, though BMR is measured under stricter conditions. Both represent the energy your body uses at rest to sustain life. Your Fitbit or smartwatch 'calories burned at rest' figure is usually an RMR estimate derived from a formula similar to Mifflin-St Jeor.
BMR varies widely by body size, age, and sex. A typical adult female may have a BMR of 1,200–1,600 kcal/day, while a typical adult male may range from 1,500–2,000 kcal/day. Taller, heavier, and younger individuals generally have higher BMRs.
The Mifflin-St Jeor equation is accurate within approximately ±10% for most healthy, non-obese adults. It may be less accurate for athletes with very high muscle mass, older adults with significant muscle loss, or individuals with thyroid or metabolic disorders.
BMR is measured under strict conditions (complete rest, fasted state, thermoneutral environment). RMR is measured under more relaxed conditions and is typically 10–20% higher than BMR. In practice, the terms are often used interchangeably, but RMR is more commonly measured in clinical settings.
Yes. As you lose body mass — especially muscle — your BMR decreases because there is less metabolically active tissue to maintain. This is one reason weight loss can plateau; the body requires fewer calories as it gets lighter.
Resistance training to build muscle is the most effective way to increase BMR, since muscle tissue burns more calories at rest than fat tissue. Adequate protein intake, sleep, and thyroid health also support a healthy metabolic rate.
Most nutrition professionals recommend not eating below your BMR for extended periods, as this can trigger muscle breakdown and metabolic adaptation. A registered dietitian can help you set a safe calorie target based on your goals.
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