Health & Fitness · Guide
BMR Calculator Guide: What Your Metabolism Burns at Rest
Your body burns calories even when you do nothing — breathing, pumping blood, keeping your brain working and repairing cells all cost energy. That baseline is your Basal Metabolic Rate (BMR), and it usually makes up about 60–70% of the calories you burn each day. Understanding your BMR is the foundation for every weight goal, because it tells you the floor below which eating becomes unsustainable.
In this guide
What drives your BMR
The biggest driver is lean muscle mass — muscle burns more energy at rest than fat. Age also matters: metabolism slows slightly with age, partly because muscle mass tends to decline. Weight, height and sex all feed into the estimate as well.
How the estimate works
Most modern calculators use the Mifflin-St Jeor equation, which combines age, sex, weight and height into a calorie-per-day number. It is accurate enough for planning when you treat the result as a starting estimate rather than an exact measurement — the only exact way is lab testing.
Using BMR for weight goals
BMR is the base, not your total need. Add daily activity to get your maintenance calories, then eat slightly below that to lose weight or above it to gain muscle. Tracking a few weeks of weight change tells you whether your true number is higher or lower than the estimate.
Key takeaways
- BMR is 60–70% of your daily calorie burn.
- Muscle mass is the biggest controllable driver.
- The Mifflin-St Jeor formula estimates it reliably.
- Use BMR as the base, then add activity for maintenance.
Frequently asked questions
What is a normal BMR?
A typical adult BMR ranges from roughly 1,200 to 1,800 calories per day, varying with size, muscle mass, age and sex. The calculator gives your personal estimate.
Is BMR the same as maintenance calories?
No. BMR is resting burn only. Maintenance calories add the energy you spend moving and exercising, and are what you eat to keep weight steady.
Why does BMR drop with age?
Muscle mass tends to decline with age, and muscle burns more calories than fat. Strength training and adequate protein help preserve it and keep BMR higher.
Put these numbers to work
BMI, BMR, daily calories, ideal weight and body fat — instantly.
BMR Calculator
Calculate your Basal Metabolic Rate with the Mifflin-St Jeor equation.
Daily Calorie Calculator
Calculate the calories you need to maintain, lose or gain weight.
Body Fat Calculator
Estimate body fat percentage with the U.S. Navy method.
BMI Calculator
Calculate your Body Mass Index and healthy weight range.