# What is my BMR?

Estimates basal metabolic rate (calories a day at rest) with the Mifflin-St Jeor, revised Harris-Benedict, or Katch-McArdle equation, and daily energy needs at three activity levels.

- Page: https://www.acalculator.org/health/bmr-calculator
- JSON spec: https://www.acalculator.org/health/bmr-calculator.json
- Version: 708925acf36f

## Default answer

Example with the default inputs (Weight 180 lb, Height 5 ft 10 in, Age 30, Body fat 15%, Sex Male, Formula Mifflin-St Jeor (1990)): With the Mifflin-St Jeor (1990) formula, your BMR is about 1,783 calories a day.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| bodyWeight | Weight | Your body weight. |
| height | Height | Your height without shoes. Katch-McArdle does not use it. |
| age | Age | Your age in whole years. Katch-McArdle does not use it. |
| bodyFat | Body fat | Your body fat as a percent of body weight. Only Katch-McArdle uses it. |
| bmr | BMR (calories a day) | Basal metabolic rate: kilocalories a day the body uses at complete rest. |
| sex | Sex | Sex at birth. Mifflin-St Jeor and Harris-Benedict use it. |
| formula | Formula | The equation used to estimate BMR. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| weight | Weight | Your body weight. |
| height | Height | Your height without shoes. Katch-McArdle does not use it. |
| age | Age | Your age in whole years. Katch-McArdle does not use it. |
| bodyFat | Body fat | Your body fat as a percent of body weight. Only Katch-McArdle uses it. |
| bmr | Your BMR | Basal metabolic rate: kilocalories a day the body uses at complete rest. |
| sedentary | Sedentary or light activity (PAL 1.53) | Daily energy need at physical activity level 1.53 (FAO/WHO/UNU sedentary example): BMR × 1.53. |
| active | Active or moderately active (PAL 1.76) | Daily energy need at physical activity level 1.76 (FAO/WHO/UNU active example): BMR × 1.76. |
| vigorous | Vigorously active (PAL 2.25) | Daily energy need at physical activity level 2.25 (FAO/WHO/UNU vigorous example): BMR × 2.25. |

## Method

Mifflin-St Jeor: BMR = 10W + 6.25H − 5A + 5 (men) or − 161 (women). Harris-Benedict (Roza and Shizgal 1984): 88.362 + 13.397W + 4.799H − 5.677A (men), 447.593 + 9.247W + 3.098H − 4.330A (women). Katch-McArdle: 370 + 21.6 × W × (1 − body fat ÷ 100). W in kg, H in cm, A in years.

## Assumptions

- The equations estimate the energy used at complete rest for healthy adults; a measured value can differ.
- Katch-McArdle uses lean body mass (weight × (1 − body fat ÷ 100)), so it ignores sex, age, and height.
- Daily energy needs are BMR × the physical activity level (PAL) of the FAO/WHO/UNU (2004) examples: 1.53, 1.76, and 2.25.

## Worked examples

1. bodyWeight = 81.646627, height = 1.778, age = 30, bodyFat = 15%, sex = male, formula = mifflin-st-jeor gives bmr = 1,782.716266, active = 3,137.580628. Source: Mifflin et al. (1990) men: 10 × 81.6466266 kg + 6.25 × 177.8 cm − 5 × 30 + 5 = 1,782.72.
2. bodyWeight = 60, height = 1.65, age = 40, bodyFat = 30%, sex = female, formula = mifflin-st-jeor gives bmr = 1,270.25, sedentary = 1,943.4825. Source: Mifflin et al. (1990) women: 10 × 60 + 6.25 × 165 − 5 × 40 − 161 = 1,270.25.
3. bodyWeight = 70, height = 1.75, age = 30, bodyFat = 15%, sex = male, formula = harris-benedict gives bmr = 1,695.667. Source: Revised Harris-Benedict (Roza and Shizgal 1984) men: 88.362 + 13.397 × 70 + 4.799 × 175 − 5.677 × 30 = 1,695.67.
4. bodyWeight = 55, height = 1.6, age = 25, bodyFat = 25%, sex = female, formula = harris-benedict gives bmr = 1,343.608. Source: Revised Harris-Benedict (Roza and Shizgal 1984) women: 447.593 + 9.247 × 55 + 3.098 × 160 − 4.330 × 25 = 1,343.61.
5. bodyWeight = 80, height = 1.8, age = 30, bodyFat = 20%, sex = male, formula = katch-mcardle gives bmr = 1,752.4, vigorous = 3,942.9.
6. bmr = 1,800, height = 1.8, age = 30, bodyFat = 15%, sex = male, formula = mifflin-st-jeor gives bodyWeight = 82.

## FAQ

### What is BMR (Basal Metabolic Rate)?

BMR is the amount of energy (calories) your body burns at rest to maintain basic life functions like breathing, circulation, cell production, nutrient processing, protein synthesis, and ion transport. It represents the minimum number of calories needed to keep your body functioning while at complete rest.

### Which BMR formula should I use?

The Mifflin-St Jeor equation is recommended for most people. A 2005 review by the American Dietetic Association found it the most likely of the common equations to estimate resting energy within 10% of the measured value. The Harris-Benedict equation (1918, revised in 1984) is the traditional formula. The Katch-McArdle formula uses lean body mass, so it suits people who know their body fat percentage.

### How accurate are BMR calculations?

BMR calculations are estimates based on statistical data. In the 2005 review above, Mifflin-St Jeor came within 10% of the measured value for most, but not all, healthy adults, and individual variations can be larger due to factors like genetics, muscle mass, and metabolic conditions. For the most accurate results, consider consulting a healthcare professional or using specialized equipment.

### What are the activity levels?

Your total daily energy need is BMR × your physical activity level (PAL). The FAO/WHO/UNU (2004) report groups lifestyles as sedentary or light activity (PAL 1.40 to 1.69), active or moderately active (1.70 to 1.99), and vigorous or vigorously active (2.00 to 2.40). The calculator shows the report's example values: 1.53, 1.76, and 2.25.

### How does age affect BMR?

BMR typically decreases with age due to loss of muscle mass and changes in body composition. This is why the formulas include age as a factor - older individuals generally have lower metabolic rates than younger people with similar body compositions.

### Why is sex included in BMR calculations?

Men typically have higher BMR than women due to generally higher muscle mass and different body composition. The Mifflin-St Jeor and Harris-Benedict formulas have separate versions for men and women. Katch-McArdle uses lean body mass instead.

### How does body fat percentage affect BMR?

Muscle tissue is more metabolically active than fat tissue, so individuals with higher muscle mass and lower body fat typically have higher BMR. The Katch-McArdle formula specifically accounts for this by using lean body mass in its calculation.

### Can I use BMR for weight loss planning?

Yes, BMR is the starting point. To lose weight, you need to eat fewer calories than your total daily energy need (BMR × activity level). Talk to a doctor or registered dietitian about a safe target for you.

### What factors can affect my actual BMR?

Several factors can affect your actual BMR: muscle mass (more muscle = higher BMR), genetics, thyroid function, body temperature, stress levels, pregnancy, certain medications, and extreme dieting (which can lower BMR).

### How often should I recalculate my BMR?

Recalculate your BMR when there are significant changes in your weight, body composition, age, or activity level.

## Sources

- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. https://doi.org/10.1093/ajcn/51.2.241
- 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. https://doi.org/10.1093/ajcn/40.1.168
- Harris JA, Benedict FG. A biometric study of human basal metabolism. Proc Natl Acad Sci USA. 1918;4(12):370-373. https://doi.org/10.1073/pnas.4.12.370
- McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. Lippincott Williams & Wilkins (Katch-McArdle equation, 370 + 21.6 × lean body mass).
- Frankenfield D, Roth-Yousey L, Compher C. 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. https://doi.org/10.1016/j.jada.2005.02.005
- FAO/WHO/UNU. Human energy requirements. Report of a Joint FAO/WHO/UNU Expert Consultation, 2004, chapter 5 (physical activity levels). https://www.fao.org/4/y5686e/y5686e07.htm