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What is BMR (Basal Metabolic Rate)?

BMR or Basal Metabolic Rate is the minimum number of calories your body needs to perform basic functions while at complete rest. These basic functions include breathing, blood circulation, brain function, body temperature regulation, and cell regeneration. BMR accounts for approximately 60-75% of total daily energy expenditure (TDEE). The remainder comes from physical activity (30%) and food digestion (10%). Knowing your BMR is essential for diet planning, as it helps calculate how many calories you can consume to lose, gain, or maintain weight. Kalkulab's BMR Calculator uses the Mifflin-St Jeor formula, which is recognized as the most accurate method for calculating BMR. This formula takes into account weight, height, age, and gender to produce more precise results compared to older formulas like Harris-Benedict.

Mifflin-St Jeor (Most Accurate) Formula

Men: BMR = (10 × W) + (6.25 × H) - (5 × A) + 5Formula: Women: BMR = (10 × W) + (6.25 × H) - (5 × A) - 161

Variables:

  • WBody Weight
    In kilograms (kg)(e.g.: 70 kg)
  • HHeight
    In centimeters (cm)(e.g.: 175 cm)
  • AAge
    In years(e.g.: 25 years)

Categories:

< 1200 kcalLow BMR (Small women)
1200 - 1600 kcalNormal BMR (Moderate)
1600 - 2000 kcalHigh BMR (Men/Active)
> 2000 kcalVery High BMR (Athletes)

How to Use the KalkuLab BMR Calculator

  1. 1

    Enter Personal Data

    Enter age (years), gender, height (cm), and weight (kg) accurately.

  2. 2

    Select Gender

    BMR formulas differ: men use +5 constant, women use −161 due to body composition differences.

  3. 3

    Click Calculate

    The system computes BMR using the Mifflin-St Jeor formula automatically.

  4. 4

    Interpret Results

    Results show calories burned at complete rest for basic bodily functions only.

Examples

Example 1: Woman Starting a Diet

Problem:

Lisa (35), 160 cm, 143 lb. What is her BMR?

Solution:
  1. 1.Female formula: (10×65) + (6.25×160) − (5×35) − 161 = 1314 kcal
Result:1314 kcal/day

Minimum 1314 kcal for basic functions. Diet target ≈ TDEE − 400 kcal.

Example 2: Fitness Athlete

Problem:

Tom (25), 175 cm, 154 lb, very active. BMR?

Solution:
  1. 1.Male formula: 1674 kcal/day
Result:1674 kcal/day

For bulking: TDEE ≈ 1674 × 1.725 + 500 ≈ 3400 kcal/day.

Example 3: Underweight Student

Problem:

Chris (20), 172 cm, 115 lb. BMR?

Solution:
  1. 1.Male formula: 1500 kcal/day
Result:1500 kcal/day

Target ~2800 kcal/day with high protein to gain weight.

Example 4: Maintenance

Problem:

Emma (30), 155 cm, 121 lb, moderate activity. BMR?

Solution:
  1. 1.Female formula: 1208 kcal/day
Result:1208 kcal/day

Maintenance ≈ 1208 × 1.55 ≈ 1870 kcal/day.

Example 5: Senior

Problem:

George (65), 165 cm, 137 lb. BMR?

Solution:
  1. 1.Male formula: 1331 kcal/day
Result:1331 kcal/day

Avoid large deficits; maintenance ≈ 1830 kcal/day.

Frequently Asked Questions

What is BMR and why does it matter?
BMR is calories needed for breathing, circulation, brain function, and temperature regulation at rest. Knowing BMR helps plan diets for weight loss, muscle gain, or maintenance.
Why does this calculator use Mifflin-St Jeor?
It is considered the most accurate BMR formula for healthy adults, validated scientifically and recommended by nutrition organizations.
How do I use this BMR calculator?
Enter age, gender, height, and weight. Results show baseline resting calorie needs instantly.
Is BMR the same as TDEE?
No. BMR is 60–75% of total daily energy. TDEE = BMR × activity factor (1.2 sedentary to 1.9 very active).
Who can use this calculator?
Adults aged 18–80 for diet and fitness planning. Not recommended for children, pregnant/nursing women, or certain medical conditions without doctor advice.
How does BMR relate to weight loss?
Calculate TDEE from BMR, then subtract 300–500 kcal for safe loss of 0.5–1 kg per week without harming basic functions.
How often should I recalculate BMR?
Recalculate after ±5 kg weight change, every 5–10 years of age, or significant body composition shifts—typically every 3–6 months.
Why do BMR formulas differ for men and women?
Men have more muscle mass; muscle burns more calories at rest. Mifflin-St Jeor uses +5 for men and −161 for women.

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References