BMI / BMR Calculator
Compute Body Mass Index and basal metabolic rate (Mifflin-St Jeor).
Overview
The BMI / BMR Calculator gives you two numbers in one shot: Body Mass Index from your height and weight, and basal metabolic rate from the Mifflin-St Jeor formula. Together they paint a quick picture of where you sit on the standard health charts and roughly how many calories your body burns at rest.
It is useful for anyone tracking general fitness, dietitians sketching a baseline for clients and health-tech developers prototyping calorie features. The result is not a diagnosis — it is a starting point for a conversation with a real clinician.
How it works
BMI is weight / height^2 in metric units (kg / m^2). The standard WHO categories are underweight (<18.5), normal (18.5-24.9), overweight (25-29.9) and obese (>=30). It does not account for muscle versus fat, so very muscular people score high BMIs without being unhealthy.
Mifflin-St Jeor BMR for men is 10 * weight_kg + 6.25 * height_cm - 5 * age + 5. For women it is 10 * weight_kg + 6.25 * height_cm - 5 * age - 161. Multiply BMR by an activity factor (1.2 sedentary, 1.55 moderate, 1.9 very active) to estimate total daily calories.
Examples
Height 175 cm, weight 70 kg
→ BMI ≈ 22.9 (normal)
Male, 30y, 180 cm, 80 kg
→ BMR ≈ 1780 kcal/day
→ Moderate activity ≈ 2760 kcal/day
Female, 25y, 165 cm, 60 kg
→ BMR ≈ 1370 kcal/day
→ Sedentary ≈ 1644 kcal/day
Height 5'10", weight 200 lb
→ BMI ≈ 28.7 (overweight)
FAQ
Is BMI accurate for athletes?
No. Muscle is denser than fat, so an athlete with low body fat can score in the overweight range. Use body composition for a fairer assessment.
Which BMR formula is best?
Mifflin-St Jeor is the modern standard and slightly more accurate than the older Harris-Benedict equation for typical adults.
Does BMR change with age?
Yes — it tends to fall a little each decade due to muscle loss. The formula already includes age as a term.
Imperial or metric input?
Both are accepted; the tool converts pounds and inches to kilograms and centimetres internally.
Should I use BMR or TDEE to plan calories?
Plan around total daily energy expenditure (TDEE), which is BMR multiplied by an activity factor. BMR alone is what you burn lying still.