What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body burns at rest to keep basic functions running, such as breathing, circulation, cell production, and temperature regulation. Even if you stayed in bed all day, your body would burn these calories just to stay alive. BMR is the single largest component of the calories you burn every day, usually making up about 60% to 75% of total daily expenditure.
Understanding your BMR is the foundation for planning weight loss, weight gain, or weight maintenance. Because weight change is driven by the balance between calories consumed and calories burned, knowing your resting burn rate gives you a reliable baseline for deciding how many calories to eat. Trying to manage weight without this number is like budgeting without knowing your income.
How to Use the BMR Calculator
Getting your BMR and daily calorie needs takes only a moment. Enter your basic details and choose the activity level that matches your lifestyle.
- Enter your age, sex, weight in kilograms, and height in centimeters.
- Select the activity level closest to your typical week, from sedentary to extra active.
- Click “Calculate BMR” to see your BMR and estimated daily maintenance calories.
- Review the weight-loss calorie suggestions shown with the result.
The Mifflin-St Jeor Equation
This calculator uses the Mifflin-St Jeor equation, which is widely considered one of the most accurate equations for estimating BMR. It is based on age, sex, weight, and height:
- Male: 10 × weight(kg) + 6.25 × height(cm) – 5 × age + 5
- Female: 10 × weight(kg) + 6.25 × height(cm) – 5 × age – 161
The difference between the sexes comes from the fact that men typically carry more muscle mass, which burns more calories at rest. Age matters because metabolism tends to slow with age, and the formula reflects that with the age component.
Daily Calorie Needs (TDEE)
Your BMR is only part of the picture. To estimate how many calories you burn in a full day, the calculator multiplies your BMR by an activity factor, giving you your Total Daily Energy Expenditure, or TDEE. The standard factors are:
- Sedentary (little 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
- Extra active (physical job or heavy training): 1.9
A Worked Example
To see the formula in action, take a 30-year-old man who weighs 75 kg and is 175 cm tall. His BMR is 10 × 75 + 6.25 × 175 – 5 × 30 + 5, which works out to 750 + 1093.75 – 150 + 5 = about 1699 calories per day. If he is moderately active (factor 1.55), his TDEE is about 1699 × 1.55 = 2633 calories per day, which is what he needs to maintain his weight. For weight loss at 500 calories below maintenance, his target would be around 2133 calories per day.
Compare that with a 30-year-old woman of the same weight and height. Her BMR is 10 × 75 + 6.25 × 175 – 5 × 30 – 161 = about 1533 calories per day. The roughly 166-calorie gap comes almost entirely from the different constant in the formula, reflecting the fact that men typically carry more muscle mass, which burns more calories at rest.
Using the Numbers for Weight Goals
To Maintain Weight
Eat around your TDEE. At this intake, the calories you consume match the calories you burn, so your weight stays roughly stable.
To Lose Weight
Eat below your TDEE. A deficit of about 500 calories per day typically produces a sustainable loss of roughly 0.5 kg per week. The calculator shows what your intake looks like at deficits of 250 and 500 calories.
To Gain Muscle
Eat slightly above your TDEE while training, usually a surplus of a few hundred calories, so your body has the energy to build new tissue.
Factors That Affect BMR
Several factors influence how fast your resting metabolism runs. Muscle mass is the most important controllable factor, because muscle burns more calories at rest than fat. Age reduces BMR over time, which is why staying active and preserving muscle matters more as you get older. Genetics, hormones, and body size also play roles. Because these vary, your true BMR can differ by a few percent from any formula estimate.
BMR vs. Resting Metabolic Rate (RMR)
You may also hear the term resting metabolic rate, or RMR. The two are similar but not identical. RMR is usually measured under less strict conditions and tends to come out slightly higher than BMR, because it includes some energy used for food digestion and minor movement. In practice, the numbers are close, and the Mifflin-St Jeor equation is used for both. For everyday calorie planning, the difference is small enough that you can treat them as interchangeable.
Why BMR Changes as You Lose Weight
BMR is not a fixed number; it falls as you lose weight. A lighter body has less tissue to maintain, so it burns fewer calories at rest. A 75 kg person who drops to 70 kg will have a lower BMR, which means the same calorie intake now creates a smaller deficit.
This is one reason weight loss often slows after the first few weeks, and why the calculator is designed to be used again after significant changes. The effect is partly offset by preserving muscle, because muscle burns more calories at rest than fat.
Beyond the Number: What Your BMR Doesn’t Tell You
Calorie targets are useful, but they are not the whole story. Where your calories come from matters for appetite, energy, and long-term success. Protein, for example, is more satiating and helps preserve muscle during weight loss, while highly processed foods are easy to overeat. A sensible approach pairs the calorie targets from this calculator with a balanced diet rich in protein, vegetables, and whole foods, plus regular strength training to keep your metabolism working efficiently.
Tips for Accurate Results
- Enter your current weight in kilograms, not a goal weight.
- Be honest about your activity level; overestimating gives misleading calorie targets.
- Recalculate after significant weight changes, since BMR falls as you lose weight.
- Combine calorie targets with strength training to protect muscle while dieting.
- Track your weight over a few weeks and adjust intake if the scale moves too fast or too slowly.
Why Use This BMR Calculator?
- Uses the accurate Mifflin-St Jeor equation
- Five activity levels for a realistic TDEE
- Shows calorie targets for maintenance and weight loss
- Free and unlimited use
- No registration or data uploads
- Works on any device with a browser