What BMR tells you
Your Basal Metabolic Rate is the number of calories your body burns just to keep you alive — breathing, pumping blood, repairing cells and regulating temperature — if you spent the whole day at complete rest.
BMR typically accounts for 60–70% of the calories you burn each day, which makes it the single biggest piece of your energy budget. Everything else — moving around, exercising, even digesting food — stacks on top of this baseline. That's why BMR is the starting point for any sensible calorie plan: you can't know how much to eat until you know how much you burn doing nothing.
How BMR is calculated
This calculator uses the Mifflin-St Jeor equation, which research has repeatedly found to be the most accurate predictive formula for most adults. It uses your weight, height, age and sex:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
We also show the revised Harris-Benedict result for comparison, since it's the formula many older tools still use. The two usually land within a few percent of each other.
What changes your BMR
BMR isn't fixed — several factors push it up or down:
- Muscle mass. Muscle is metabolically active, so more lean tissue means a higher BMR. This is the strongest lever you can actually control.
- Age. BMR gradually falls with age, partly because we tend to lose muscle over time.
- Sex. Men usually have a higher BMR thanks to greater average muscle mass.
- Body size. A larger body has more tissue to maintain and burns more at rest.
Turning BMR into a calorie plan
BMR alone won't tell you how much to eat, because nobody lies in bed all day. Multiply it by an activity factor to get your Total Daily Energy Expenditure (TDEE) — the real number you eat around. Our calorie calculator does this automatically and gives you targets for losing, maintaining or gaining weight. From there, the macro calculator splits your calories into protein, carbs and fat.
Helpful tools to track your progress
Track weight and trends over time.
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Frequently asked questions
What's the difference between BMR and TDEE?
BMR is what you burn at complete rest. TDEE is BMR multiplied by an activity factor and represents your real total daily burn including movement and exercise.
Which BMR formula is most accurate?
For most adults the Mifflin-St Jeor equation is considered the most accurate, which is why this calculator uses it as the headline result.
Can I lose weight by eating below my BMR?
It's not recommended. Eating below your BMR for long periods can be unsustainable and may slow your metabolism. Aim for a moderate deficit below your TDEE instead.
Does building muscle raise my BMR?
Yes. Muscle tissue burns more calories at rest than fat, so increasing lean mass through strength training gradually raises your BMR.