Basal Metabolic Rate (BMR) is the energy your body burns at complete rest, just to keep you alive — heart beating, lungs breathing, organs functioning. The calculator uses the Mifflin-St Jeor equation, currently the most accurate BMR formula for adults of all body sizes.
What is BMR Calculator?
Your body burns calories all day even when you do nothing. About 60-75% of total daily calorie burn happens just keeping organs, brain, immune system, and muscles ticking over. That baseline is your BMR. The remaining 25-40% comes from activity — walking, exercise, even fidgeting.
The Mifflin-St Jeor equation, developed in 1990, replaced the older Harris-Benedict formula as the standard because it more accurately reflects modern body composition. The calculator uses this formula. It needs four inputs: gender, age, height, and weight. Body fat percentage and lean mass would make it more accurate still, but require special equipment.
BMR is the foundation for all calorie calculations. Multiplying BMR by an activity factor (1.2 for sedentary, up to 1.9 for very active) gives Total Daily Energy Expenditure (TDEE) — the calories you actually burn in a day. From there, eat at TDEE to maintain weight, below to lose, above to gain.
The Mifflin-St Jeor equation
- kg
- Body weight—in kilograms
- cm
- Height—in centimetres
- age
- Age—in years
How to use this calculator
Pick gender, enter age, height, and weight. The calculator returns BMR plus TDEE estimates at five activity levels.
Pick your gender
Required for the formula's offset (+5 vs −161). The difference comes from average body composition between sexes.
Enter your age
BMR drops about 1-2% per decade after age 20 due to natural muscle loss.
Enter height in cm
Use a precise measurement; small errors compound in the result.
Enter weight in kg
Use morning weight, post-bathroom, with minimal clothing. Most accurate baseline.
Read BMR + TDEE estimates
BMR is the headline. The activity multipliers below show your TDEE at sedentary, lightly, moderately, very, and extra active lifestyles.
What BMR is good for
Setting calorie goals
Multiply BMR by activity factor to get TDEE, then adjust ±500 kcal/day for weight loss/gain.
Weight loss planning
Eating below BMR for extended periods is unsafe. Set a deficit by eating below TDEE, not below BMR.
Fitness apps
Most calorie-tracking apps (MyFitnessPal, HealthifyMe) calculate calorie targets from BMR and goals.
Macro split
Once you know your daily calories, divide them into protein/carbs/fat using a target ratio (40/30/30, etc.).
Plateau diagnosis
If weight loss stalls, recompute BMR with current weight. As you lose weight, BMR drops, requiring further calorie cuts.
Common mistakes to avoid
Using BMR as the calorie target
BMR is calories at rest. You need TDEE (BMR × activity factor). Eating only at BMR-level results in unintended weight loss.
Ignoring age in long-term planning
BMR drops with age. A 30-year-old's calorie target is not appropriate at 50. Recompute every few years or after major weight changes.
Glossary
- BMR
- Basal Metabolic Rate — calories burned at complete rest, in 24 hours.
- RMR
- Resting Metabolic Rate — slightly higher than BMR (~10%); includes the energy of digesting recent meals.
- TDEE
- Total Daily Energy Expenditure — BMR plus all activity-related calorie burn.
- Activity factor
- Multiplier (1.2 to 1.9) applied to BMR to estimate TDEE based on lifestyle.
- Mifflin-St Jeor
- The 1990 equation used here. Replaced the older Harris-Benedict for better accuracy.
References
- Mifflin-St Jeor original paper (1990, AJCN)— American Journal of Clinical Nutrition