What Is BMR (Basal Metabolic Rate)?

Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic physiological functions — breathing, circulation, cell production, and temperature regulation — while at complete rest. It represents the minimum energy expenditure required to keep you alive.

BMR accounts for roughly 60–75% of total daily energy expenditure for most sedentary people.

BMR vs TDEE

Term	Definition
BMR	Calories burned at complete rest (no movement)
TDEE	Total Daily Energy Expenditure — BMR × activity multiplier

Your TDEE is what you actually burn in a day. Eating at TDEE maintains weight; eating below it causes fat loss; eating above it causes weight gain.

How Is BMR Calculated?

Two equations are commonly used:

Mifflin-St Jeor (Recommended)

Considered the most accurate for most people:

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

Harris-Benedict (Revised 1984)

Slightly older, still widely used:

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

Activity Multipliers

Multiply your BMR by the factor that best matches your lifestyle to get TDEE:

Activity Level	Multiplier
Sedentary (desk job, little exercise)	× 1.2
Lightly active (1–3 days/week exercise)	× 1.375
Moderately active (3–5 days/week exercise)	× 1.55
Very active (6–7 days/week hard exercise)	× 1.725
Extra active (physical job + hard training)	× 1.9

What Affects BMR?

• Lean muscle mass — muscle burns more calories than fat at rest; higher muscle = higher BMR.
• Age — BMR typically decreases ~2% per decade after age 30.
• Sex — men generally have a higher BMR due to greater muscle mass.
• Hormones — thyroid disorders can raise (hyperthyroidism) or lower (hypothyroidism) BMR significantly.
• Diet — severe calorie restriction causes the body to reduce BMR as a survival mechanism.

Using BMR for Weight Goals

1. Calculate your BMR using the BMR Calculator.
2. Multiply by your activity level to get TDEE.
3. Subtract 300–500 kcal/day for steady, sustainable fat loss (~0.3–0.5 kg/week).
4. Add 250–500 kcal/day for gradual muscle gain.

Avoid cutting more than 1,000 kcal below TDEE — aggressive deficits cause muscle loss and metabolic adaptation.