Basal Metabolic Rate Calculator
Enter your details below. The calculator calculates your basal metabolic rate using the Harris-Benedict formula and shows daily calorie needs at three different activity levels.
Basal Metabolic Rate (BMR)
Sedentary, no exercise
Moderate exercise
Heavy exercise
What Is Basal Metabolic Rate (BMR)?
Basal Metabolic Rate (BMR) is the number of calories your body needs each day just to stay alive — even if you spent the entire day in bed. This energy fuels essential functions: breathing, blood circulation, cell repair, brain activity, and maintaining body temperature.
BMR typically accounts for 60–75% of your total daily energy expenditure (TDEE). The remainder is divided between physical activity (15–30%) and the thermic effect of food — the energy your body uses to digest meals (about 10%).
The Harris-Benedict Formula
This calculator uses the revised Harris-Benedict equation (Roza & Shizgal, 1984), one of the most widely cited BMR formulas in nutrition science.
For men:
BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age)
For women:
BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age)
Worked Example
A 30-year-old man, 5′10″ (178 cm), 176 lb (80 kg):
BMR = 88.362 + (13.397 × 80) + (4.799 × 178) − (5.677 × 30) BMR = 88.362 + 1,071.76 + 854.22 − 170.31 = 1,844 kcal/day
This means his body burns about 1,844 calories per day at complete rest.
Activity Multipliers — From BMR to TDEE
To estimate Total Daily Energy Expenditure (TDEE), multiply your BMR by an activity factor:
| Activity Level | Factor | Description | Example (BMR 1,800) |
|---|---|---|---|
| Sedentary | 1.2 | Office work, no exercise | 2,160 kcal |
| Lightly active | 1.375 | Light exercise 1–3 days/week | 2,475 kcal |
| Moderately active | 1.55 | Moderate exercise 3–5 days/week | 2,790 kcal |
| Very active | 1.725 | Hard exercise 6–7 days/week | 3,105 kcal |
| Extremely active | 1.9 | Physical job + heavy training | 3,420 kcal |
BMR by Age and Gender — Reference Table
| Age | Average Male BMR | Average Female BMR |
|---|---|---|
| 20 | 1,850 kcal | 1,450 kcal |
| 30 | 1,800 kcal | 1,400 kcal |
| 40 | 1,740 kcal | 1,360 kcal |
| 50 | 1,680 kcal | 1,310 kcal |
| 60 | 1,620 kcal | 1,260 kcal |
| 70 | 1,560 kcal | 1,210 kcal |
Values based on average height and weight for US adults.
What Affects Your BMR?
Several factors influence your basal metabolic rate:
- Muscle mass — Muscle burns more calories at rest than fat. Strength training raises BMR.
- Age — Metabolism declines roughly 1–2% per decade after age 20, largely due to muscle loss.
- Gender — Men generally have higher BMR due to greater muscle mass and larger body size.
- Genetics — Hereditary factors can cause up to a 200 kcal/day difference between individuals.
- Thyroid function — Thyroid hormones (T3 and T4) directly regulate metabolic rate. Hypothyroidism slows BMR.
- Body temperature — A 1°F rise in body temperature increases BMR by about 7%.
- Calorie restriction — Extreme dieting can lower BMR by 20% or more (metabolic adaptation).
BMR vs. TDEE — What Is the Difference?
| BMR | TDEE | |
|---|---|---|
| Measures | Resting energy expenditure | Total daily energy use |
| Includes | Breathing, circulation, cell repair | BMR + exercise + food digestion |
| Use for | Understanding baseline metabolism | Setting calorie targets for weight goals |
If you want a complete calorie target for weight loss, maintenance, or muscle gain, use the Daily Calorie Needs Calculator, which adds your activity level to your BMR.
Frequently Asked Questions
How can I increase my BMR?
Build muscle through resistance training, stay well-hydrated, get adequate sleep (7–9 hours), eat enough protein, and avoid crash diets that trigger metabolic adaptation.
Is BMR the same as resting metabolic rate (RMR)?
They are similar but not identical. RMR is measured under less strict conditions than BMR and is typically 10–20% higher. For practical purposes, the terms are often used interchangeably.
How accurate is the Harris-Benedict formula?
Studies show it is accurate within ±10% for most people. The Mifflin-St Jeor equation (1990) may be slightly more accurate for overweight individuals. Both formulas are estimates — indirect calorimetry in a lab is the gold standard.
Why does my metabolism slow with age?
Primarily due to loss of lean muscle mass (sarcopenia). Maintaining strength training as you age is the best way to counteract metabolic decline.
Related Tools
- Daily Calorie Needs Calculator — Calculate TDEE with your activity level
- Macro Calculator — Get your ideal protein, carb, and fat split
- Calorie Burn Calculator — Estimate calories burned during exercise
- BMI Calculator — Check your body mass index
- Heart Rate Calculator — Find your training zones
Sources
- Harris, J.A. & Benedict, F.G. (1918). A Biometric Study of Human Basal Metabolism. Proceedings of the National Academy of Sciences.
- Roza, A.M. & Shizgal, H.M. (1984). The Harris Benedict equation reevaluated. The American Journal of Clinical Nutrition.
- Mifflin, M.D. et al. (1990). A new predictive equation for resting energy expenditure. The American Journal of Clinical Nutrition.