What is basal metabolic rate?
Basal metabolic rate, or BMR, estimates how many calories your body uses at rest to support basic functions such as breathing, circulation, temperature regulation, and cell repair. It is not the same as the calories you burn in a normal day because daily movement and exercise are not included.
BMR is useful as a starting point for calorie planning. People often use it before estimating TDEE, setting a calorie deficit, or understanding why two people with different body sizes may need different daily energy intake.
Mifflin-St Jeor formula
This calculator uses the Mifflin-St Jeor equation, a common modern formula based on sex, age, weight, and height. The formula gives an estimate, not a lab measurement.
BMR men = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5; BMR women = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161Example BMR calculation
For a 30-year-old man who weighs 80 kg and is 180 cm tall, BMR is 10 x 80 + 6.25 x 180 - 5 x 30 + 5. That equals about 1,780 calories per day.
This number represents estimated resting energy use. A real daily calorie need would be higher after adding work, walking, training, and other activities.
BMR vs TDEE: what is the difference?
A higher BMR does not automatically mean better health. It usually reflects body size, lean mass, age, and sex. The result should be used as a planning estimate rather than a target by itself.
Why BMR changes with age
Use BMR when you want a baseline before calculating maintenance calories. It can also help compare how weight loss, weight gain, or aging may change estimated energy needs.
BMR calculator limitations
Do not treat BMR as your full daily calorie allowance. Most people need more than BMR because they move, digest food, and perform daily tasks. Also remember that formulas can be less accurate for athletes, older adults, and people with unusual body composition.
What changes the BMR Calculator result most?
The inputs that usually change BMR most are body weight, height, age, and sex. Weight and height push the estimate upward as body size increases, while age usually reduces the estimate over time in the formula. This is why the same person may need to recalculate BMR after a major weight change.
For calorie planning, BMR should normally be followed by an activity multiplier to estimate TDEE. Someone with a desk job and someone who trains daily can have similar BMR values but very different daily calorie needs.
Practical notes for the BMR Calculator
BMR can be helpful for understanding why calorie targets are not one-size-fits-all. A taller or heavier person usually has a higher estimated resting need than a smaller person, even before exercise is considered.
If you are using BMR for weight planning, compare it with TDEE rather than eating at BMR automatically. Eating too close to BMR may be inappropriate for many active people and should be considered carefully.
The result is also affected by the formula choice. Mifflin-St Jeor is widely used, but no equation knows your exact lean mass, hormones, medications, or medical history.
Frequently asked questions
Does BMR change if I lose weight?
Yes. Lower body weight usually lowers estimated BMR because there is less body tissue to support.
Is BMR the same as calories burned at rest?
It is an estimate of resting energy use, but exact resting metabolic rate requires controlled testing.
Which formula does this calculator use?
It uses the Mifflin-St Jeor equation.
How does muscle mass affect BMR?
More lean mass can increase resting energy needs, but this calculator estimates from common body measurements.