BMR Calculator

What does your BMR mean?

Your Basal Metabolic Rate of 1,649 kcal/day is the estimated energy your body uses at complete rest — before any activity, digestion, or exercise is added.

Limitations

BMR formulas are population averages. Body composition, genetics, hormone levels, and medical conditions can shift actual metabolic rate above or below this estimate.

This calculator provides general informational estimates and is not a medical diagnosis. Results should be interpreted alongside other factors. If you have concerns about your health, consider speaking with a qualified healthcare professional.

What BMR measures

Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic life functions — breathing, circulation, cell production, and organ function — while completely at rest. It represents the majority of most people's total daily calorie needs, typically 60–75%, even before accounting for any physical activity.

Common BMR formulas

W is weight in kg, H is height in cm, A is age in years. The Mifflin-St Jeor equation is generally considered more accurate for most modern populations than the older Harris-Benedict formula, though both are widely used estimates.

What influences BMR

• Muscle mass — muscle tissue burns more calories at rest than fat tissue, so higher lean mass raises BMR.
• Age — BMR tends to decline gradually with age, partly due to natural loss of muscle mass.
• Sex — men typically have higher BMR than women of the same weight, largely due to differences in average body composition.
• Body size — larger bodies generally require more energy to maintain basic functions.
• Genetics and hormones — thyroid function and genetic factors can shift BMR up or down independent of body composition.

From BMR to total daily needs

Activity level	Multiplier
Sedentary (little/no exercise)	BMR × 1.2
Lightly active (1–3 days/week)	BMR × 1.375
Moderately active (3–5 days/week)	BMR × 1.55
Very active (6–7 days/week)	BMR × 1.725

Tips

• BMR alone isn't your calorie target for weight loss or gain — multiply it by an activity factor to get TDEE first.
• Strength training over time can raise BMR by building metabolically active muscle tissue.
• Extreme calorie restriction can lower BMR as the body adapts, which is one reason very low-calorie diets often stall.

Worked examples

Example 1 — Man, 30, 80 kg, 180 cm: BMR = 10(80) + 6.25(180) − 5(30) + 5 = 800 + 1,125 − 150 + 5 = 1,780 kcal/day at complete rest.

Example 2 — Woman, 45, 65 kg, 165 cm: BMR = 10(65) + 6.25(165) − 5(45) − 161 = 650 + 1,031.25 − 225 − 161 = 1,295 kcal/day.

Example 3 — Turning BMR into a calorie target: A moderately active 1,780 kcal/day BMR (from Example 1) gives a TDEE of about 1,780 × 1.55 = 2,759 kcal/day — the calorie level needed to maintain current weight with that activity level.

Mifflin-St Jeor vs. Harris-Benedict

	Mifflin-St Jeor	Harris-Benedict
Introduced	1990	1919 (revised 1984)
General accuracy	Considered more accurate for modern populations	Tends to overestimate BMR somewhat
Inputs	Weight, height, age, sex	Weight, height, age, sex

Frequently asked questions

Is BMR the same as TDEE? No — BMR is calories at complete rest, while Total Daily Energy Expenditure (TDEE) adds activity, exercise, and digestion on top of BMR.

Why do BMR formulas give slightly different results? Each formula was derived from different study populations and variables, so small differences between methods are normal and expected.

Can I increase my BMR? Building muscle mass through resistance training is one of the few reliable ways to meaningfully raise resting metabolic rate over time.

Does BMR decrease with age even if weight stays the same? Yes — the formulas subtract a term for age because resting metabolism tends to decline gradually over the years, partly from natural muscle loss.

Should I eat exactly my BMR in calories? No — BMR only covers calories needed at complete rest. Eating at BMR alone, without accounting for daily activity, typically creates too large a calorie deficit for most people.

Why is BMR different between two people of the same weight? Differences in muscle mass, age, sex, and body composition all shift resting energy needs, so weight alone doesn't fully determine BMR.

Can a very low-calorie diet lower my BMR? Yes — prolonged, severe calorie restriction can trigger metabolic adaptation, where the body reduces its resting energy use to conserve fuel, which is one reason extreme diets often stall.

How accurate is a formula-based BMR compared to lab testing? Formulas like Mifflin-St Jeor are estimates accurate to within roughly 10% for most people; indirect calorimetry (a lab breathing test) measures actual resting energy use directly and is more precise.

Another worked example

A 28-year-old man, 178 cm, 80 kg has an estimated BMR of roughly 1,820 calories/day using the Mifflin-St Jeor formula — this is the baseline before any activity is factored in via the Calorie Calculator.

What affects the result

• Age — BMR generally declines with age, partly due to natural muscle loss.
• Sex — men typically have a higher BMR than women at the same weight, largely due to differences in average muscle mass.
• Body composition — muscle tissue burns more calories at rest than fat tissue.

How to use this calculator

1. Enter your age, sex, height, and weight.
2. Press Calculate to see your estimated Basal Metabolic Rate.

Common mistakes to avoid

• Confusing BMR with TDEE — BMR alone doesn't include any activity, so using it directly for calorie targets will significantly underestimate your real needs.
• Trying to eat below BMR for extended periods, which can be counterproductive and is generally not recommended without medical guidance.

Key terms explained

Basal Metabolic Rate (BMR): Calories burned at complete rest to maintain vital body functions.

Mifflin-St Jeor equation: A widely used formula for estimating BMR from age, sex, height, and weight.