BMR Calculator
Calculate your Basal Metabolic Rate and daily calorie needs using scientifically validated formulas
Your age affects BMR - metabolism slows with age
Enter your current body weight
Enter your height for accurate BMR calculation
Optional - enables the Katch-McArdle formula which uses lean body mass for a more personalized BMR estimate
Calculate Your BMR
Enter your details and activity level to see your basal metabolic rate, TDEE, and daily calorie targets.
How to Use the BMR Calculator
Enter Your Personal Details
Select your gender and enter your age. Gender affects BMR because men typically have more muscle mass than women, which burns more calories. Age matters because metabolism naturally slows as you get older.
Enter Your Height and Weight
Choose between imperial (lbs, feet/inches) or metric (kg, cm) units, then enter your current weight and height. These measurements are the primary factors in the BMR equations.
Select Your Activity Level
Choose the activity level that best matches your typical week. Options range from Sedentary (desk job, no exercise) to Extra Active (intense daily exercise or physical labor). Be honest to get accurate TDEE results.
Review Your BMR and TDEE Results
View your BMR from both the Mifflin-St Jeor and Harris-Benedict formulas, your TDEE (total calories burned daily), and calorie targets for weight loss or gain. The macronutrient breakdown shows suggested daily protein, carb, and fat intake in grams.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to maintain basic life functions like breathing, circulation, and cell repair. It represents your body's minimum energy requirement if you stayed in bed all day. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor that accounts for exercise and daily movement. TDEE represents the total calories you actually burn in a day. For example, if your BMR is 1,600 calories and you are moderately active (multiplier of 1.55), your TDEE would be approximately 2,480 calories. You should use TDEE, not BMR, when planning your daily calorie intake.
Which BMR formula is more accurate - Mifflin-St Jeor or Harris-Benedict?
The Mifflin-St Jeor equation is generally considered more accurate for most people and is recommended by the American Dietetic Association. It was developed in 1990 using modern population data, whereas the Harris-Benedict equation dates back to 1919 (revised in 1984). Studies show the Mifflin-St Jeor formula predicts BMR within 10% of measured values for about 82% of people, compared to about 76% for Harris-Benedict. However, both formulas provide useful estimates. We display both results so you can see the range and use the average if you prefer a middle-ground approach.
How can I use my BMR to lose weight?
To lose weight, you need to create a calorie deficit by eating fewer calories than your TDEE (not your BMR). A safe deficit is 500 calories per day, which leads to approximately 1 pound of weight loss per week since one pound of body fat equals about 3,500 calories. For example, if your TDEE is 2,400 calories, eating 1,900 calories daily should produce steady weight loss. Never eat below your BMR for extended periods, as this can slow your metabolism, cause muscle loss, and lead to nutrient deficiencies. Always consult a healthcare provider before starting any significant calorie restriction program.
Why does BMR decrease with age?
BMR decreases with age primarily because of the gradual loss of lean muscle mass, a process called sarcopenia. Starting around age 30, adults lose approximately 3-8% of muscle mass per decade if they do not engage in regular strength training. Since muscle tissue is more metabolically active than fat tissue (burning about 6 calories per pound at rest versus 2 calories per pound for fat), less muscle means fewer calories burned at rest. Hormonal changes also play a role. Levels of growth hormone and testosterone decline with age, further reducing muscle mass and metabolic rate. Regular resistance training and adequate protein intake can help slow this decline.
How accurate is a BMR calculator and what factors can affect results?
BMR calculators using the Mifflin-St Jeor equation are accurate within about 10% for most healthy adults. However, several factors can cause your actual BMR to differ from the calculated estimate. Body composition is a major factor: two people of the same weight can have very different BMRs if one has more muscle mass. Genetics, thyroid function, certain medications, and hormonal conditions also influence metabolism. Environmental factors like temperature, stress levels, and sleep quality can temporarily affect BMR. For the most precise measurement, consider indirect calorimetry testing at a medical facility. Use calculator results as a practical starting point and adjust based on real-world results over 2-4 weeks.