BMR Calculator
Your Basal Metabolic Rate is the number of calories your body burns just staying alive – breathing, circulation, cell repair. It is the foundation every calorie plan is built on.
Fill in your details and your BMR appears here instantly.
Your BMR
- kcal/day at complete rest
Daily calories at each activity level
This table is your BMR multiplied by standard activity factors – the same math behind our TDEE calculator.
What is BMR?
BMR is the energy your body needs over 24 hours at complete rest. For most people it makes up 60-75% of everything they burn in a day – far more than any workout. Muscle tissue burns more than fat tissue, which is why two people of the same weight can have meaningfully different BMRs.
The Mifflin-St Jeor equation
Introduced in 1990 and validated repeatedly since, Mifflin-St Jeor is the equation the Academy of Nutrition and Dietetics considers the most reliable for healthy adults:
Men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5Women: 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
That is exactly what this calculator runs. Note it uses weight, height, age and sex only – it does not know your body composition, so very muscular or very lean people can sit 5-10% off the estimate.
BMR vs TDEE
BMR is what you burn doing nothing. TDEE is what you burn living your actual life – BMR plus work, walking, training and digestion. Use BMR to understand your floor; use the TDEE calculator to plan what to eat, and the calorie deficit calculator to plan fat loss.
What affects your BMR
The equation works from four inputs: weight, height, age and sex. In the formula, more weight and height raise the estimate, age lowers it, and men and women get different constants. Those four inputs capture the broad differences between people, but not everything.
Two people with identical stats can still burn different amounts, because the formula cannot see muscle mass, hormones or genetics. Treat its answer as an estimate rather than a reading, and check with a doctor if your real-world results never line up with it.
BMR examples from the equation
Run a few sample profiles through Mifflin-St Jeor and the pattern shows clearly: bigger and younger means a higher burn.
| Profile | Estimated BMR |
|---|---|
| Man, 30, 180 cm, 80 kg | 1,780 kcal/day |
| Woman, 30, 165 cm, 65 kg | 1,370 kcal/day |
| Man, 50, 175 cm, 85 kg | 1,699 kcal/day |
| Woman, 50, 160 cm, 70 kg | 1,289 kcal/day |
Your own result from the calculator is worked out with exactly the same equation, so it is directly comparable with these.
Reading the activity table in your results
Under your BMR, the results table multiplies it by the five standard activity factors, from 1.2 for a desk-bound week up to 1.9 for a physical job plus training. The row closest to your typical week is a working estimate of your maintenance calories: the intake that would keep your weight roughly stable.
If two rows both sound like your life, start with the lower one, eat at that level for two to three weeks, and let your weekly average weight settle the question. The TDEE calculator jumps straight to this step, and the calorie deficit calculator plans a loss from it.
Frequently asked questions
Can I raise my BMR?
Slowly, yes. Building muscle is the most reliable lever, and eating enough protein supports it. Drastic dieting does the opposite – severe restriction can lower measured expenditure, one reason crash diets stall.
Is it safe to eat below my BMR?
BMR on its own cannot tell you what is safe to eat. It estimates resting energy use, not an intake prescription, and the right target for you depends on your size, activity and health history. Very low calorie diets are not suitable or safe for everyone, and NHS guidance says they should only be followed with professional support. For a personal answer, speak to a doctor or registered dietitian.
Why does BMR drop with age?
Mostly because of gradual muscle loss and hormonal change. The decline is roughly 1-2% per decade after early adulthood, and strength training blunts a large part of it.
How accurate is this number?
Typically within about 10% of a lab measurement for healthy adults. Track your weight for two to three weeks at a calculated intake and adjust from real data.
Is BMR the same thing as metabolism?
Not quite. Metabolism is the set of chemical processes that keeps your body running and turns food into energy. BMR measures one part of it: the energy you would expend at complete rest. Moving around, exercising and even digesting food all add on top of BMR, which is why two people with the same BMR can burn very different totals in a day.
Does this calculator use metric or imperial units?
Both. Use the Units toggle at the top of the calculator to switch between imperial (feet/inches and pounds) and metric (centimetres and kilograms). The result is shown in calories either way.
Disclaimer
This page provides estimates for general information only, not medical advice. No equation can capture your full health picture, so talk to a doctor or registered dietitian before making major changes to how you eat, especially if you are pregnant, under 18, or managing a condition such as diabetes.