What Is BMR?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to keep you alive — breathing, circulating blood, repairing cells, regulating temperature. It excludes digestion and any physical activity, representing the absolute minimum energy your body needs in a 24-hour period.

BMR typically accounts for 60-75% of the total calories most people burn in a day, making it the single biggest factor in calorie needs — bigger than exercise for most non-athletes. Understanding your BMR is the foundation for setting accurate calorie targets, whether the goal is weight loss, maintenance, or muscle gain.

The Formula (Mifflin-St Jeor)

Men: BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161
W = weight in kg | H = height in cm | A = age in years

Worked Example

A 35-year-old woman weighing 68 kg (150 lb) and standing 165 cm (5'5") tall: BMR = (10 × 68) + (6.25 × 165) − (5 × 35) − 161 = 680 + 1,031.25 − 175 − 161 = 1,375 calories/day. That's the energy her body needs just lying in bed all day doing nothing.

Activity LevelMultiplierEstimated TDEE
Sedentary (little/no exercise)×1.21,650 cal
Lightly active (1-3 days/wk)×1.3751,891 cal
Moderately active (3-5 days/wk)×1.552,131 cal
Very active (6-7 days/wk)×1.7252,372 cal

This second number — TDEE, or Total Daily Energy Expenditure — is what most people actually need for weight maintenance, since it factors in real-world activity on top of the baseline BMR.

Why BMR Matters for Weight Goals

Eating consistently below BMR (not just below TDEE) is generally discouraged, since it can signal the body to conserve energy, potentially slowing metabolism and increasing muscle loss risk. A moderate calorie deficit relative to TDEE — typically 300-500 calories/day — is the more commonly recommended approach for sustainable weight loss.

Figures above are illustrative estimates only, not medical advice. Consult a healthcare provider or registered dietitian for personalized guidance.

Frequently Asked Questions

What does BMR stand for?

BMR stands for Basal Metabolic Rate — the number of calories your body burns at complete rest just to keep vital functions like breathing, circulation, and cell repair running.

What is the difference between BMR and TDEE?

BMR is calories burned at total rest with zero activity. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor, giving your actual estimated calorie needs.

What formula calculates BMR most accurately?

The Mifflin-St Jeor equation is widely considered the most accurate modern formula, more precise than the older Harris-Benedict equation for most adults.

Does muscle mass affect BMR?

Yes, significantly. Muscle tissue burns more calories at rest than fat tissue, so two people of the same weight but different body composition can have noticeably different BMRs.

Should I eat below my BMR to lose weight faster?

Generally not recommended. Eating below BMR for extended periods can slow metabolism and cause muscle loss; most guidance suggests eating at or above BMR with a moderate deficit below TDEE instead.

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