Health Hub · Free tool
BMR Calculator
Your basal metabolic rate is the energy your body burns at complete rest — the engine idling. Calculate yours with the Mifflin-St Jeor equation, and learn what genuinely moves it.
This is your resting burn only. To see your full daily needs with activity included — and targets for losing or gaining — take this number to our calorie calculator.
What is basal metabolic rate?
BMR is the energy cost of simply being alive: heart beating, lungs breathing, brain thinking (about 20% of the total on its own), liver and kidneys filtering, cells rebuilding, body staying at 37°C. For most adults it's 1,200–2,000 calories a day — 60 to 75% of everything you burn. Exercise, for all its virtues, is the minority shareholder in your energy budget; the engine idle is the majority.
How to calculate BMR
This tool uses the Mifflin-St Jeor equation, the most accurate of the standard formulas in validation studies:
| Formula | |
|---|---|
| Men | (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5 |
| Women | (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161 |
It estimates within about 10% for most people. (You may also see "RMR" — resting metabolic rate — a slightly looser measurement taken in less strict conditions; for practical purposes the numbers are interchangeable.)
What actually affects your metabolism
- Muscle mass — the big lever. Muscle burns several times more energy at rest than fat, which is why strength training changes your idle burn in a way cardio doesn't.
- Age: BMR drifts down a few percent per decade — largely because of muscle loss, which makes the fix obvious.
- Size and sex: bigger bodies burn more; men average higher through muscle and size.
- Genetics and hormones: real but usually modest — with one exception worth naming: an underactive thyroid genuinely lowers BMR and is testable. Persistent exhaustion, cold intolerance and unexplained weight gain deserve a GP blood test, not a supplement.
How to speed up your metabolism — honestly
What works: build muscle (two or three strength sessions a week), eat enough protein (digesting it costs 20–30% of its own calories — the highest of any food), and move more between workouts — the fidgeting-walking-stairs layer called NEAT varies hugely between people and dwarfs most "metabolism boosters". What doesn't, meaningfully: green tea, chilli, cold showers and "fat-burner" supplements — effects measured in single-digit calories. And crash dieting works against you: very low intakes cost muscle, which lowers BMR — the yo-yo mechanism in one sentence.
Put your number to work
BMR is the foundation, not the plan. Your real daily budget is BMR times activity — our calorie calculator builds it and adds safe targets, and the BMI calculator tells you whether changing weight deserves the effort at all. Wondering whether a medicine or supplement is affecting your weight or energy? Ask our pharmacist — it's free.
Frequently asked questions
Should I eat below my BMR to lose weight?
No — deficits come off your total daily burn (TDEE), not your resting rate. Eating below BMR for long stretches is crash-diet territory: muscle loss, rebound, misery.
Why is my BMR lower than my friend's?
Size, muscle, age and sex explain nearly all of it. Same-size people differ far less than diet culture suggests — usually by a sandwich, not a feast.
Does skipping meals slow your metabolism?
Not meaningfully in the short term — "starvation mode" from a missed lunch is a myth. Chronic severe under-eating is a different story, via muscle loss.