BMR Calculator — Know Your Basal Metabolic Rate for Better Nutrition Planning
The BMR Calculator estimates how many calories your body burns at complete rest—breathing, circulation, and basic cell function. That number is the foundation of your total daily energy needs. Knowing your BMR helps you understand why calorie recommendations vary from person to person and how to tailor intake for weight maintenance, loss, or gain. BMR is the largest part of most people's daily energy use, so getting a good estimate is the first step to understanding how much you should eat. This article explains what BMR is, how the calculator works, and how to use the result together with activity to plan your nutrition.
What Does This Tool Do?
This tool calculates your Basal Metabolic Rate (BMR)—the calories you use in a day if you did nothing but rest. It uses the Mifflin–St Jeor equation, which takes your weight, height, age, and sex and returns an estimate in calories per day. BMR does not include activity; it is the baseline. To get total daily needs, you multiply BMR by an activity factor (as in our Calorie Needs calculator). BMR varies with body size, composition, age, and sex. The result is an estimate, not a lab measurement, but it is one of the most widely used and validated formulas for adults. Researchers and dietitians often prefer Mifflin–St Jeor over older formulas because it tends to be more accurate across different ages and body types. Once you have your BMR, you can multiply it by 1.2 for sedentary, 1.55 for moderate activity, or other factors to get your total daily energy expenditure.
How to Use It (Step-by-step)
Men: BMR = 10×weight(kg) + 6.25×height(cm) - 5×age + 5Women: BMR = 10×weight(kg) + 6.25×height(cm) - 5×age - 161- 1Step 1:
Enter your weight in kilograms (kg).
- 2Step 2:
Enter your height in centimetres (cm).
- 3Step 3:
Enter your age in years.
- 4Step 4:
Select your sex (male or female). The Mifflin–St Jeor formula uses different constants for each.
- 5Step 5:
Click Calculate.
- 6Step 6:
Read your BMR—e.g. 'BMR: about 1,450 calories/day.'
- 7Step 7:
Use it as the base for daily needs. Multiply by an activity factor (e.g. 1.2 for sedentary, 1.55 for moderate activity) to estimate total calories, or use our Calorie Needs calculator which does this for you.
Key Features
The calculator uses the Mifflin–St Jeor equation, which is well validated and often preferred over older formulas. It requires only weight, height, age, and sex. Results are in calories per day, rounded to a whole number. The tool is free and does not store data. It is intended for adults; BMR in children and teens is calculated differently. It does not account for body composition, hormones, or medical conditions—use it as a general reference. No activity level is needed for BMR; that is added when you move to total daily needs. You can recalculate when your weight or age changes to see how your baseline metabolism might shift over time.
Use Cases
You might use the BMR calculator when: you want to understand how many calories you burn at rest; you are using the number to build your own activity multipliers for total daily needs; you are comparing your intake to your estimated BMR to see if you are under- or overeating at rest; you are learning how age, size, and sex affect metabolism; or you are preparing for a conversation with a dietitian or doctor about calorie targets. It is less useful as a standalone number without activity—for a full daily target, use the Calorie Needs calculator or multiply BMR by an activity factor. People on very low calorie diets sometimes check that they are not eating far below BMR for long periods. Coaches use BMR as the first step in building custom calorie plans for athletes and clients.
FAQ
BMR is calories at total rest. TDEE (Total Daily Energy Expenditure) is BMR plus all activity (walking, exercise, etc.). TDEE is usually BMR multiplied by a factor between about 1.2 and 1.9 depending on activity.
Metabolism tends to slow with age, partly due to changes in muscle mass and hormone levels. The formula includes age to reflect this general trend.
Building muscle through resistance training can increase the calories you burn at rest. The formula does not change with muscle mass, so a muscular person's true BMR may be higher than the formula suggests.
Short-term, many people can eat below BMR and still function. Long-term very low intake can be harmful. For sustained weight loss, a modest deficit (often 250–500 kcal below total needs, not necessarily below BMR) is usually safer. A dietitian can help design a plan.
On average, men have more lean mass (muscle and other non-fat tissue) per kilogram of body weight, which burns more calories at rest. The formula uses different constants for each sex to reflect this.