If you've ever tried to lose weight, gain muscle, or just eat healthier, you've probably run into the words "calories" and "BMR" and wondered what they actually mean for your body. The truth is, your metabolism isn't some mysterious force - it's a measurable, predictable system. Once you understand how it works, managing your weight stops being guesswork.
Our Calorie & BMR Calculator uses the Mifflin-St Jeor equation, which is the most accurate formula for estimating basal metabolic rate. It was developed in 1990 and has been validated by dozens of studies since. Here's what the numbers mean for you.
BMR - What Your Body Burns Doing Nothing
Your Basal Metabolic Rate is the number of calories your body needs just to stay alive - breathing, circulating blood, maintaining body temperature, and keeping your organs functioning. If you stayed in bed all day, this is what you'd burn. For most people, BMR accounts for about 60-75% of total daily calorie burn. Factors that affect BMR include age (it decreases as you get older), muscle mass (more muscle = higher BMR), gender (men typically have higher BMR due to more muscle mass), and genetics.
TDEE - Your Real-World Calorie Burn
Total Daily Energy Expenditure adds physical activity into the equation. It's BMR multiplied by an activity factor based on how much you move during the day. A desk worker who doesn't exercise has a TDEE much lower than a construction worker who hits the gym five times a week. This is the number that matters for weight management - eating at maintenance keeps your weight stable, eating below it leads to weight loss, and eating above it leads to weight gain.
The 500-Calorie Rule
A deficit of about 500 calories per day from your maintenance level typically leads to about 0.5 kg (1 lb) of weight loss per week. This is considered a safe, sustainable rate. Much faster than that, and you're likely losing muscle and water, not just fat.
Why Privacy Matters for Health Data
Your body measurements are some of the most personal data you have. Our calculator runs entirely in your browser. Your age, weight, height, and activity level never leave your device. No accounts, no tracking, no data collection. Just a clean calculation that respects your privacy.