How to Calculate Your BMR (Basal Metabolic Rate)
By Jesse · Last updated July 16, 2026
Your Basal Metabolic Rate is the number of calories your body needs to stay alive at complete rest — breathing, circulating blood, maintaining body temperature, and repairing cells, with no movement at all. It is the single largest component of how many calories you burn in a day, typically making up 60 to 75 percent of your total energy expenditure. Understanding it is the foundation for any calorie-based diet plan.
The two main formulas
Two equations dominate practical BMR calculation. Both require the same four inputs: sex, age, height, and body weight.
Mifflin-St Jeor (1990)
This is the most widely recommended formula for healthy adults. A 2005 analysis in the Journal of the American Dietetic Association found it to be more accurate than competing equations for most non-obese adults.
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Harris-Benedict (revised 1984)
The original Harris-Benedict equations date to 1919. Roza and Shizgal revised them in 1984 with a larger dataset. This version tends to run about 5 percent higher than Mifflin-St Jeor.
Men: BMR = 88.362 + 13.397 × weight(kg) + 4.799 × height(cm) − 5.677 × age
Women: BMR = 447.593 + 9.247 × weight(kg) + 3.098 × height(cm) − 4.330 × age
Which formula to use
For most purposes, Mifflin-St Jeor is the better starting point. If you want a second opinion, run both and average the results — the average smooths out the slight bias each formula carries at different body compositions. The BMR calculator on this site does exactly that.
A worked example
Take a 35-year-old woman, 168 cm tall, weighing 68 kg.
Mifflin-St Jeor:
BMR = 10 × 68 + 6.25 × 168 − 5 × 35 − 161
BMR = 680 + 1050 − 175 − 161 = 1394 kcal/day
That is how many calories her body would burn lying still all day. Her actual daily needs are higher once activity is added.
BMR vs TDEE: what is the difference?
BMR is your calorie burn at complete rest. TDEE — Total Daily Energy Expenditure — adds the calories you burn through daily movement and structured exercise. TDEE is your maintenance level: the calories needed to keep your weight stable. You get there by multiplying your BMR by an activity factor:
| Activity level | Multiplier |
|---|---|
| Sedentary (little or no exercise) | 1.2 |
| Lightly active (1-3 days/week) | 1.375 |
| Moderately active (3-5 days/week) | 1.55 |
| Very active (6-7 days/week) | 1.725 |
| Athlete (twice-daily training) | 1.9 |
For the example above (BMR 1394 kcal, moderately active): TDEE = 1394 × 1.55 = approximately 2160 kcal/day. The TDEE calculator handles this in one step.
What affects your BMR
BMR is primarily driven by body size and composition. Larger, heavier people have more tissue to maintain and burn more calories at rest. Muscle is metabolically more expensive than fat, so two people of the same weight but different body compositions will have different BMRs. Age lowers BMR gradually — mostly because people tend to lose muscle as they get older, not because of age itself.
Extended calorie restriction also lowers BMR beyond what weight loss alone would predict — a process called metabolic adaptation. The body becomes more efficient, which is why weight loss often plateaus on a fixed intake. Maintaining muscle through resistance training and adequate protein helps limit this effect.
How to use your BMR
BMR is the input, not the output. Use it to calculate your TDEE, then set your intake relative to that number based on your goal:
- Weight loss: eat below TDEE (typically 300-700 kcal less per day for a sustainable deficit).
- Maintenance: eat at TDEE.
- Weight gain: eat above TDEE (typically 200-500 kcal above for lean bulking).
For a full plan with macros, use the macro calculator. To set a goal weight and timeline, use the body weight planner.
These are estimates for healthy adults, not medical advice. BMR formulas have a margin of error of roughly 10 percent for most people and wider margins for those with unusual body compositions. See our methodology for the sources behind these calculations.