# BMR Calculator

- **URL:** https://codeasystem.com/calculators/health/bmr-calculator/
- **Category:** health
- **Description:** Estimate your basal metabolic rate; the calories your body burns at complete rest; using Mifflin-St Jeor with a revised Harris-Benedict comparison.
- **Primary output:** Basal metabolic rate (Mifflin-St Jeor): 1,780 kcal/day

## Inputs
- Sex (name: `sex`, type: select)
- Weight (name: `weight`, type: number, example: 80)
- Height (name: `height`, type: number, example: 180)
- Age (name: `age`, type: number, example: 30)

## Outputs
- Basal metabolic rate (Mifflin-St Jeor): 1,780 kcal/day
- Revised Harris-Benedict estimate: 1,854 kcal/day
- Equation used: Mifflin-St Jeor (men)

## Formula / methodology
```
Men:   BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161
(W kg, H cm, A years)
```

The primary estimate uses the Mifflin-St Jeor equation, published in 1990 and validated by the American Dietetic Association as the most accurate predictive formula for resting metabolic rate in the general adult population.

A revised Harris-Benedict row shows the older classic equation for comparison. When the two agree closely you can be confident in the estimate; wide gaps usually reflect unusual body compositions.

## Assumptions & limitations
- Healthy adult with typical body composition.
- Measured at true rest; no digestion, exercise or stress.
- Estimate only; indirect calorimetry is the clinical gold standard.

## How to use
1. **Select sex**; The equations differ by a constant term calibrated separately for men and women.
2. **Enter weight, height and age**; Use metric units: kilograms for weight, centimetres for height, whole years for age.
3. **Compare the two rows**; The main figure is Mifflin-St Jeor; the second row shows the revised Harris-Benedict value for reference.

## Example
A 30-year-old man weighing 80 kg at 180 cm has a Mifflin-St Jeor BMR of about 1,780 kcal/day; the energy his body spends simply keeping organs running.

Result for these inputs:

```
Basal metabolic rate (Mifflin-St Jeor): 1,780 kcal/day
```

## About this calculator
### What BMR actually represents

Your basal metabolic rate covers breathing, circulation, cell repair, hormone production and brain function; typically 60–70% of total daily energy expenditure in sedentary people. It is the floor beneath every activity multiplier.

### Why age matters

The −5A term subtracts five calories per year of age. Muscle mass tends to decline with age, and since muscle is metabolically expensive tissue, resting burn falls accordingly; one reason appetite needs shift decade by decade.

### From BMR to real life

- Multiply BMR by an activity factor (1.2–1.9) to reach TDEE.
- Never eat below BMR for extended periods without professional guidance.
- Recheck after significant weight changes of more than ~5 kg.

## FAQs
### Which formula should I trust?

Mifflin-St Jeor; ADA reviews found it within 10% of measured values more often than Harris-Benedict. We show both so you can see the spread.

### Is BMR the same as RMR?

Nearly. Resting metabolic rate is measured under slightly less strict conditions and typically runs a few percent higher than strict basal rate.

### Why does BMR drop when I diet?

Adaptive thermogenesis: prolonged deficits lower hormone levels and spontaneous movement, reducing actual expenditure below what static equations predict.

> **Disclaimer:** This calculator is for general educational purposes only and does not constitute professional advice.

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Last updated: 2026-08-23 · Version: 1.0.0 · [HTML version](https://codeasystem.com/calculators/health/bmr-calculator/)