BMR Calculator (Basal Metabolic Rate)

BMR stands for Basal Metabolic Rate, the calories your body burns just to stay alive while completely at rest. Breathing, heartbeat, body temperature regulation, organ function, brain activity. If you stayed in bed all day and didn’t move, you’d still burn this many calories.

BMR typically accounts for 60-75% of your total daily calorie burn. The rest comes from movement, exercise, and the small amount of energy used to digest food.

Two Formulas (This Calculator Uses Both)

The result shows numbers from both equations so you can compare.

Mifflin-St Jeor (1990), the recommended one:

• Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
• Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161

Original Harris-Benedict (1919), widely used historically:

• Men: BMR = 88.362 + (13.397 × weight kg) + (4.799 × height cm) − (5.677 × age)
• Women: BMR = 447.593 + (9.247 × weight kg) + (3.098 × height cm) − (4.330 × age)

Mifflin-St Jeor is more accurate for modern populations and is what most current sports nutrition references use. Harris-Benedict was derived from a small early-twentieth-century sample and tends to overestimate by roughly 5%. If the two numbers on your result disagree by more than that, check your inputs.

BMR Versus TDEE

TDEE stands for Total Daily Energy Expenditure, what you actually burn in a normal day. TDEE = BMR × an activity factor:

This calculator shows your TDEE at every level so you can see the range.

What Affects BMR

• Age. BMR drops about 2% per decade after 20, mostly through lost muscle rather than anything metabolic
• Sex. Men typically run higher, from more muscle and less essential fat
• Lean mass. Muscle burns roughly 6 calories per pound per day at rest, fat about 2. Worth being honest about the size of this: adding five pounds of muscle, which is a hard year of training, buys you around 30 calories a day. Half a banana. Lift for the strength and the body composition, not for the metabolic bonus
• Genetics. Real BMR varies 10-15% from what these formulas predict, so some people genuinely do run hotter or cooler than the equation says
• Hormones. Thyroid disorders, testosterone and cortisol all shift the number, sometimes a long way

Worked Example

30-year-old woman, 65 kg, 165 cm:

BMR (Mifflin-St Jeor) = (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 650 + 1,031.25 − 150 − 161 = 1,370 kcal/day

For comparison, Harris-Benedict on the same inputs:

BMR = 447.593 + (9.247 × 65) + (3.098 × 165) − (4.330 × 30) ≈ 1,430 kcal/day, about 60 kcal higher

Most reliable real-world test: track your weight and food intake for two weeks at maintenance. The number that keeps your weight stable is your true TDEE. Divide by your activity multiplier and you have your real BMR.

Do Not Eat At Your BMR

This is the mistake the number invites, and it is worth stating plainly. BMR is what you would burn unconscious in a hospital bed. Eating at that level while walking around, working and training puts you in a deficit far larger than the one you intended, and the body responds by shedding muscle alongside fat and quietly reducing spontaneous movement, which drags your actual expenditure down with it.

The floor most clinicians use is roughly 1,200 calories a day for women and 1,500 for men, and even those are only sensible short-term and with attention to protein. A deficit of 300 to 500 below your TDEE, not your BMR, is the range that shows up in the research as sustainable.