BMR Calculator: Your Basal Metabolic Rate Explained

Your Basal Metabolic Rate (BMR) is the calories your body needs just to stay alive — heart beating, lungs breathing, brain functioning — without any movement whatsoever. It is the foundation of all calorie calculations.

How to use the BMR calculator

1. Enter your age, sex, weight and height
2. Select your preferred formula (Mifflin-St Jeor recommended)
3. Click Calculate

The Mifflin-St Jeor formula

Men: BMR = (10 x weight kg) + (6.25 x height cm) minus (5 x age) + 5 Women: BMR = (10 x weight kg) + (6.25 x height cm) minus (5 x age) minus 161

This is the most accurate formula endorsed by the Academy of Nutrition and Dietetics.

Real examples

25-year-old woman, 65kg, 165cm: BMR = (10 x 65) + (6.25 x 165) minus (5 x 25) minus 161 = 650 + 1031.25 minus 125 minus 161 = 1,395 calories per day

35-year-old man, 85kg, 178cm: BMR = (10 x 85) + (6.25 x 178) minus (5 x 35) + 5 = 850 + 1112.5 minus 175 + 5 = 1,792 calories per day

What affects your BMR?

• Body size: Larger bodies require more energy at rest.
• Age: BMR decreases roughly 1-2% per decade from age 20.
• Sex: Men typically have higher BMR due to greater muscle mass.
• Body composition: More muscle means higher BMR than the same weight with more fat.
• Hormones: Thyroid hormones significantly regulate metabolic rate.

From BMR to daily calorie needs

• Sedentary: BMR x 1.2
• Lightly active (1-3x/week): BMR x 1.375
• Moderately active (3-5x/week): BMR x 1.55
• Very active (6-7x/week): BMR x 1.725
• Extra active: BMR x 1.9

This gives your TDEE. Use our TDEE calculator for the full breakdown.

Can you increase your BMR?

Build muscle through resistance training. Each kilogram of muscle burns approximately 13 calories at rest versus 4.5 for fat.

Do not crash diet. Very low calorie intake causes your body to lower metabolic rate as a survival mechanism.

Frequently asked questions

Is BMR the same as resting metabolic rate? Closely related but technically different. BMR is measured under strict conditions. RMR is more practical. They typically differ by less than 10%.

Does BMR decrease on a diet? Yes. Calorie restriction causes some muscle loss and the body lowers metabolic rate. This adaptation is stronger with more severe restriction.

My BMR seems lower than expected. Is something wrong? Many people over-estimate their BMR. If you suspect a medical issue especially thyroid function, speak with your doctor.

Can I rely on BMR to set calorie intake? BMR is just the starting point. You need to account for all activity to get daily needs. Never eat below your BMR without medical supervision.

How does BMR change during pregnancy? BMR increases as the body supports fetal growth. Energy needs increase by approximately 300 calories per day in second and third trimesters.