What is a BMR Calculator?
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to perform its most basic (basal) life-sustaining functions — breathing, circulation, cell production, and nutrient processing — if you were to rest completely for 24 hours. Think of it as the energy your body burns just to keep you alive.
This Harris-Benedict BMR calculator uses the revised Harris-Benedict equation to calculate your BMR and then multiplies it by your activity factor to give you your Total Daily Energy Expenditure (TDEE) — the real number of calories you need each day.
Disclaimer: This tool is for informational purposes only and cannot replace professional medical advice. If you have health concerns, please consult a physician or registered dietitian.
How Can You Calculate Your BMR?
Calculating your basal metabolic rate requires four inputs:
- Weight — in kilograms (metric) or pounds (imperial)
- Height — in centimetres (metric) or feet and inches (imperial)
- Age — in years
- Biological sex — male or female (the formulas differ)
What is the Harris-Benedict Equation?
The Harris-Benedict Equation, originally published in 1919 and revised in 1984, is one of the most widely used formulas for estimating BMR. The revised (Roza & Shizgal) version is:
For Men:
BMR = 66.5 + (13.75 × weight in kg) + (5.003 × height in cm) − (6.75 × age)
For Women:
BMR = 655.1 + (9.563 × weight in kg) + (1.850 × height in cm) − (4.676 × age)
When using imperial measurements, this calculator automatically converts your weight and height to metric before applying the formula.
How to Find Your Total Daily Calorie Needs
To determine your TDEE (Total Daily Energy Expenditure), multiply your BMR by the appropriate activity factor:
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Little or no exercise | × 1.2 |
| Lightly Active | Light exercise / sports 1–3 days/week | × 1.375 |
| Moderately Active | Moderate exercise / sports 3–5 days/week | × 1.55 |
| Very Active | Hard exercise / sports 6–7 days/week | × 1.725 |
| Extra Active | Very hard exercise + physical job | × 1.9 |
| Professional Athlete | Training as a professional athlete | × 2.3 |
Using Your BMR for Weight Management
Once you know your TDEE (maintenance calories), you can use it as a reference point:
- Lose weight — eat approximately 500 calories below your TDEE per day (≈ 0.5 kg / 1 lb per week loss)
- Maintain weight — eat at your TDEE
- Gain weight — eat approximately 500 calories above your TDEE per day (≈ 0.5 kg / 1 lb per week gain)
Frequently Asked Questions
Is BMR the same as TDEE?
No. BMR is the number of calories you burn at complete rest. TDEE accounts for your physical activity and is always higher than BMR. Use TDEE — not BMR — as your daily calorie target.
How accurate is the Harris-Benedict equation?
The Harris-Benedict equation is a good general estimate but may be off by 10–15% for individuals with very high or very low body-fat percentages. The Mifflin-St Jeor equation is sometimes considered slightly more accurate for the general population, while the Katch-McArdle formula is better if you know your lean body mass.
Why are the formulas different for men and women?
Men typically have a higher proportion of lean muscle mass compared to women of the same height and weight. Muscle tissue burns more calories than fat tissue at rest, so men generally have a higher BMR.
Does BMR change with age?
Yes. BMR tends to decrease with age, primarily because lean muscle mass decreases as we get older (sarcopenia). This is why maintaining muscle through strength training becomes increasingly important as you age.
Can I use this calculator to plan a diet?
This calculator gives you a useful starting point. However, individual metabolism varies, and factors like hormones, sleep quality, stress levels, and medical conditions can all affect your actual calorie needs. Always consult a healthcare professional or registered dietitian before making significant dietary changes.