BMR Calculator

BMR is the calories your body burns at complete rest, while TDEE is BMR plus everything you do during the day. BMR covers only life-sustaining functions, as if you stayed in bed without moving. TDEE (Total Daily Energy Expenditure) adds all activity on top: walking, working, exercising, and even fidgeting. TDEE is usually estimated by multiplying BMR by an activity factor: Sedentary (x1.2), Light (x1.375), Moderate (x1.55), Very active (x1.725), or Extreme (x1.9). TDEE is the figure that reflects what you need to eat to maintain your current weight, whereas BMR is your resting baseline. Both are estimates, so treat the activity multipliers as approximate starting points.

BMR tends to decline gradually with age, largely because we lose muscle mass and undergo hormonal changes over time. The age term is built directly into the Mifflin-St Jeor equation, which subtracts more for older adults. The main driver is the age-related loss of lean muscle, known as sarcopenia, since muscle burns more energy at rest than fat does. Shifts in hormones can also play a role. The practical takeaway is that someone in their fifties generally has a somewhat lower resting calorie need than they did in their twenties at the same weight. This is one reason strength training becomes increasingly valuable with age, as maintaining muscle helps support metabolic rate.

Yes, modestly, and the most reliable approach is building and maintaining muscle mass. Because lean tissue is more metabolically active than fat, increasing muscle gradually raises the calories your body burns at rest, though the day-to-day effect is smaller than many people expect. Strength training, adequate protein intake, and quality sleep all support muscle maintenance and growth, which in turn supports your resting metabolism. Regular physical activity also raises your total daily energy expenditure even when it doesn't change BMR dramatically. Crash dieting has the opposite effect, since losing muscle along with fat can lower your rate. For personalized targets, consult a registered dietitian or healthcare professional.

Eating well below your BMR for extended periods can work against your health and your goals, so it is generally not recommended without medical supervision. Very low intakes can prompt the body to conserve energy, and prolonged severe restriction is associated with muscle loss, fatigue, nutrient deficiencies, and hormonal disruption. A suppressed metabolism can also make weight regain more likely once the diet ends. For most people, safe weight loss comes from a moderate calorie deficit set below your TDEE rather than below your resting baseline, allowing steady progress while still meeting nutritional needs. If you are considering a very low-calorie diet or have an underlying health condition, talk to a doctor or registered dietitian first.

Use Mifflin-St Jeor for most situations, which is the formula this calculator highlights. It was identified by the American Dietetic Association as the most reliable predictive equation for the general population, relying on weight, height, age, and sex. If you know your body fat percentage from a method like calipers or a DEXA scan, the Katch-McArdle formula may suit you better because it factors in lean body mass directly. The older Harris-Benedict equation remains useful as a point of comparison. Estimates can differ somewhat between formulas, so treat any single number as an approximation rather than an exact value, and confirm with a professional if you need precise figures for a medical reason.