BMR Calculator

About BMR Calculator

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain essential functions—breathing, circulation, cell repair, and nervous system operation. Calculating BMR is foundational to understanding your energy needs and making informed decisions about nutrition, fitness, and weight management.

Our BMR Calculator uses the Mifflin-St Jeor equation, one of the most accurate modern formulas, and optionally estimates your Total Daily Energy Expenditure (TDEE) based on activity level. This foundation empowers you to design sustainable nutrition plans and track progress toward health goals.

Frequently Asked Questions

Why should I know my BMR?

BMR is the foundation for calculating calorie needs. It enables accurate TDEE estimation and sustainable nutrition planning for any goal.

What's the difference between BMR and RMR?

BMR is measured under strict lab conditions (fasted, complete rest). RMR is measured in typical conditions and is slightly higher. Used interchangeably in practice.

Is Mifflin-St Jeor more accurate than Harris-Benedict?

Mifflin-St Jeor was developed using modern populations and typically provides closer estimates. Both are estimates; individual variation always exists.

How do I increase my BMR?

Build lean muscle through resistance training, ensure adequate protein/sleep, manage stress, maintain consistent activity. Each kg of muscle raises BMR modestly.

Why does my BMR decrease when I lose weight?

Weight directly enters the BMR formula. Additionally, aggressive deficits trigger adaptive thermogenesis where the body conserves energy.

Can I eat below my BMR?

Short-term yes, but chronically eating below BMR risks muscle loss, nutrient deficiency, hormonal disruption. Use moderate deficits (10-25% below TDEE) for sustainability.

How does thyroid function affect BMR?

Thyroid hormones regulate metabolic rate. Hypothyroidism reduces BMR; hyperthyroidism elevates it. Discuss thyroid screening if results seem off.

How often should I recalculate BMR?

After ~5% weight change or significant lifestyle shifts (new training, medication). Quarterly or semi-annual checks suffice for most people.

Does age affect BMR?

Yes. BMR declines ~2-8% per decade after 30 due to lean muscle loss and hormonal changes. Resistance training and adequate protein help offset decline.

What is TDEE and how does it differ from BMR?

TDEE is BMR multiplied by activity factor. It estimates total daily calorie burn including exercise, NEAT, and digestion. Use TDEE to create deficits or surpluses.