Complete guide
Reviewed July 2026Your Basal Metabolic Rate (BMR) is the number of calories your body burns doing absolutely nothing - lying still, awake, in a comfortable room. It powers your heart, brain, lungs, kidneys and the constant repair of cells, and for most people it is 60-70% of everything they burn in a day.
Because it's the foundation of your total energy needs, BMR is the starting point for any calorie plan. This calculator uses the Mifflin-St Jeor equation - the most accurate general-population formula, and the one dietitians rely on - to estimate your BMR from weight, height, age and sex.
Below: the formula with every variable explained, worked examples, how BMR becomes your daily calorie target, why it declines with age, and how to raise it.
What BMR is and how it's calculated
Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5 Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161
BMR measures the energy of simply being alive. It's distinct from your total burn, which adds movement, exercise and the energy used to digest food. Think of BMR as your body's idle fuel consumption - the engine running while parked.
The variables
- Weight (kg): more body mass needs more energy to maintain - the biggest driver.
- Height (cm): taller bodies have more tissue and surface area, raising BMR.
- Age (years): BMR falls with age (the -5 x age term), mainly from muscle loss.
- Sex: men average more lean muscle, so the male formula adds 5 while the female subtracts 161.
Worked examples
- Man, 30, 80 kg, 178 cm: BMR = 10x80 + 6.25x178 - 5x30 + 5 = 800 + 1112.5 - 150 + 5 = 1,767 kcal.
- Woman, 30, 65 kg, 165 cm: BMR = 10x65 + 6.25x165 - 5x30 - 161 = 650 + 1031.25 - 150 - 161 = 1,370 kcal.
- Same woman at 50: subtract 5 x 20 more = 1,270 kcal - about 100 kcal/day lower purely from age.
From BMR to daily calories
BMR alone isn't what you eat - you multiply it by an activity factor to get your Total Daily Energy Expenditure (TDEE), which is your maintenance calories. Then adjust up or down for your goal.
| Activity level | Factor | TDEE (maintenance) |
|---|---|---|
| Sedentary | x 1.2 | 1,644 kcal |
| Lightly active | x 1.375 | 1,884 kcal |
| Moderately active | x 1.55 | 2,124 kcal |
| Very active | x 1.725 | 2,363 kcal |
Using this calculator and raising your BMR
- Enter weight, height, age and sex accurately - small errors shift the result.
- Read your BMR, then multiply by your activity factor (or use the calorie calculator) for maintenance.
- Set a deficit or surplus from the TDEE figure, keeping intake at or above BMR.
- Recalculate after notable weight change - a lighter body has a lower BMR.
How to raise (or protect) your BMR
- Build muscle: resistance training adds lean tissue, the most metabolically active mass - the single most durable way to raise BMR.
- Eat enough protein: it costs more energy to digest and preserves muscle in a deficit.
- Avoid crash diets: aggressive under-eating lowers BMR by burning muscle and triggering adaptation.
- Stay active daily: non-exercise movement (NEAT) adds to total burn even if it isn't strictly BMR.
Frequently asked questions
Glossary
- BMR
- Basal Metabolic Rate - calories burned at complete rest.
- TDEE
- Total Daily Energy Expenditure - BMR x activity factor.
- Mifflin-St Jeor
- The most accurate general-population BMR equation.
- RMR
- Resting Metabolic Rate - like BMR but measured under looser conditions; slightly higher.
- Lean mass
- Muscle and organ tissue; the main driver of BMR.
- Metabolic adaptation
- The fall in energy use that can follow prolonged under-eating.
- NEAT
- Non-Exercise Activity Thermogenesis - energy from daily movement outside workouts.
- Activity factor
- The 1.2-1.9 multiplier converting BMR to TDEE.
Key takeaways
BMR is your at-rest calorie burn - 60-70% of daily energy - estimated most accurately by the Mifflin-St Jeor equation. It's the base for calorie planning: multiply by an activity factor for TDEE (maintenance), then adjust for your goal, keeping intake at or above BMR. BMR falls with age and weight loss, mainly through muscle loss, so build and protect muscle and recalculate as your body changes.
Enter your stats above for your BMR; then multiply by your activity level for maintenance calories - and note how 20 years of age alone changes the number.