What it is
Basal metabolic rate (BMR) is the energy a person expends at rest to maintain basic physiological function. This calculator uses the Mifflin-St Jeor equation — the best-validated predictive resting-energy equation in adults — and multiplies it by an activity factor to estimate total daily energy needs.
The formula
Mifflin-St Jeor uses weight (kg), height (cm) and age (years), with a sex-specific constant:
- Base = (10 × weight) + (6.25 × height) − (5 × age)
- Male BMR = Base + 5
- Female BMR = Base − 161
That gives BMR in kcal/day. To estimate total daily energy expenditure, multiply by an activity factor:
| Activity level | Factor |
|---|---|
| Sedentary | ×1.2 |
| Light | ×1.375 |
| Moderate | ×1.55 |
| Active | ×1.725 |
| Very active | ×1.9 |
The tool accepts age 15–80 years, height 100–250 cm and weight 30–300 kg.
When to use it
For estimating maintenance calorie needs in adolescents and adults — nutrition counselling, weight-management targets, or a starting point for dietary planning. It is a baseline estimate, not a measured value; indirect calorimetry remains the reference standard when precision matters.
Worked example
A 30-year-old male, 175 cm, 70 kg:
- Base = (10 × 70) + (6.25 × 175) − (5 × 30) = 700 + 1093.75 − 150 = 1643.75
- Male BMR = 1643.75 + 5 = ≈1649 kcal/day
- Moderate activity (×1.55) ≈ 2556 kcal/day
A female of the same dimensions would be 161 + 5 = 166 kcal/day lower at base.
Pitfalls
- Adult equation — not validated in children. Do not apply it to prepubertal patients; use age-appropriate paediatric energy methods (e.g. Schofield / WHO equations, DRI estimated energy requirements) instead. The tool’s lower age bound is 15 years for this reason.
- Predicted, not measured. Equations carry meaningful error in the very obese, the very lean, the critically ill, and athletes.
- Activity factors are coarse. They smooth over real variation in occupational and exercise expenditure — treat the total as a starting estimate to be titrated.
- BMR ≠ total energy expenditure; remember to apply the activity multiplier when counselling on intake.
Run it: Basal Metabolic Rate (BMR)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.