BMR Calculator (Basal Metabolic Rate)
Work out the energy your body spends doing nothing but keeping you alive.
Short answer: BMR (basal metabolic rate) is the energy your body would spend even if you rested all day — for breathing, circulation, cell repair and brain activity. It typically accounts for 50% to 70% of your total daily expenditure. Eating at your BMR is not a target; the figure is the starting point for working out your actual daily needs.
- Total on a sedentary day (×1.2) —
- Total on a moderate day (×1.55) —
- Total on a very active day (×1.725) —
This result is an estimate based on published formulas and is not medical advice.
Fill in the fields above to see your result. Everything updates automatically as you change the values.
What does BMR measure?
BMR is the energy your body spends maintaining its basic functions. Most of it goes to work you never notice: your heart beating, your lungs working, body temperature held steady, cells repaired. The brain alone consumes around a fifth of it.
This page uses the Mifflin-St Jeor equation:
- Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Every term says something: weight and height stand for body size, age for the lean mass that declines with it. The sex difference reflects average differences in body composition.
Should I eat at my BMR?
No. This is the most misunderstood part of BMR. It is only your resting expenditure; from the moment you get out of bed you spend energy on top of it.
Eating at BMR continuously means living in a substantial deficit without realising it. It looks like fast weight loss in the short term, but carries a risk of muscle loss, fatigue and nutrient deficiency. Your daily target should be set from your TDEE, not your BMR.
What affects BMR — and what does not
Genuine factors: body size (the largest by far), lean muscle mass, age, sex, genetics and hormonal conditions such as thyroid function.
Overstated factors: meal frequency does not change BMR — eating six times a day does not "speed up" your metabolism. The effect of green tea, chilli and similar foods is measurable but negligible in practice. Building muscle does raise BMR, but 1 kg of muscle contributes only about 10-15 kcal a day; 5 kg is ~50-75 kcal. Useful, but not an effect that drives weight loss on its own.
Example figures
How basal metabolic rate falls with age at the same weight and height. This is the numerical version of the «why does BMR fall with age» section above.
| Profile | 25 yrs | 40 yrs | 55 yrs |
|---|---|---|---|
| Female · 60 kg · 165 cm | 1,345 | 1,270 | 1,195 |
| Female · 75 kg · 165 cm | 1,495 | 1,420 | 1,345 |
| Male · 75 kg · 178 cm | 1,743 | 1,668 | 1,593 |
| Male · 90 kg · 178 cm | 1,893 | 1,818 | 1,743 |
This table shows example profiles, not your own result. Enter your details in the calculator above to get yours. Figures come from the Mifflin-St Jeor equation and are estimates.
Frequently asked questions
What is BMR?
BMR is the daily energy your body spends at complete rest on basic life functions: breathing, circulation, maintaining body temperature and cell renewal.
What is the difference between BMR and RMR?
RMR (resting metabolic rate) is a closely related measure taken under looser conditions, and typically comes out 5-10% higher than BMR. In everyday use the two are treated as interchangeable and the practical difference is negligible.
What happens if I eat below my BMR?
Briefly, nothing much. Sustained intake below BMR carries a risk of muscle loss, fatigue, hormonal disruption and nutrient deficiency. Set your target from TDEE — BMR multiplied by an activity factor — rather than from BMR itself.
Why does BMR fall with age?
Mainly because lean muscle mass declines, and muscle burns more energy than fat tissue. The age term in the equation reflects that average decline. Resistance training slows it by preserving muscle.
How much does muscle raise BMR?
About 10-15 kcal per day per kilogram of muscle. Gaining 5 kg of muscle means roughly 50-75 kcal a day. Real but small; the main benefits of building muscle are body composition and health, not metabolism.
Sources
- Mifflin MD, St Jeor ST et al. — A new predictive equation for resting energy expenditure in healthy individuals (1990)
- National Academies of Sciences — Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Protein and Amino Acids (2005)
- World Health Organization — Healthy diet
- USDA FoodData Central — Food composition database
Last updated: · This tool is for general information only. Consult a doctor or registered dietitian if you are pregnant, breastfeeding, managing a chronic condition or taking medication.