BMR Calculator – Find Your Basal Metabolic Rate
Calculate your Basal Metabolic Rate (BMR) using three peer-reviewed equations: Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle. Your BMR is the foundation of every calorie target.
Understanding your BMR
Your Basal Metabolic Rate represents the calories your body burns at complete rest, simply to stay alive. It is the largest single component of your daily energy expenditure.
What affects BMR?
- Lean body mass — the most important driver. More muscle means more idle energy demand.
- Sex — men typically have higher BMR due to greater muscle mass and lower body fat.
- Age — BMR slowly drops with age, mostly due to muscle loss (not the metabolism itself).
- Genetics — there is roughly a ±10% individual variation around the predicted average.
- Hormones — thyroid, leptin and reproductive hormones modulate BMR significantly.
Why we offer three formulas
No single formula is perfect for every body. The three options on this page were chosen because each is more accurate for a particular user profile:
- Mifflin-St Jeor — best for the general adult population.
- Harris-Benedict (revised 1984) — kept for historical comparison.
- Katch-McArdle — most accurate for lean and athletic individuals because it uses lean body mass directly.
Common questions
What is BMR?
Basal Metabolic Rate is the energy your body needs to keep its essential systems running while at complete rest — heart, lungs, brain, kidneys, and basal cellular activity. BMR makes up roughly 60–75% of your daily calorie burn.
How is BMR different from RMR?
BMR is measured under strict laboratory conditions (after a 12-hour fast, fully rested, in a thermoneutral room). Resting Metabolic Rate (RMR) is measured in less strict conditions and is typically 10–20% higher. Most online calculators that label themselves "BMR" actually estimate values closer to RMR.
Which formula is most accurate?
Mifflin-St Jeor is the most accurate predictive equation for the general adult population. Katch-McArdle is more accurate for lean, athletic individuals because it uses lean body mass directly rather than total weight. Harris-Benedict is older and tends to overestimate BMR by 5%.
Can I increase my BMR?
The biggest practical lever is adding lean muscle mass through resistance training — every kg of muscle adds about 13 kcal/day. Adequate sleep, sufficient protein intake, NEAT, and avoiding aggressive crash diets also help protect or raise BMR over time.