Understanding Your Basal Metabolic Rate (BMR)

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep you alive — breathing, circulating blood, maintaining temperature, running your organs. For most people, it’s the single largest chunk of daily calorie expenditure, and understanding it clarifies everything else.

BMR vs TDEE

BMR is what you’d burn lying still all day. Your TDEE (Total Daily Energy Expenditure) is BMR plus digestion, daily movement and exercise. BMR is usually 60–70% of TDEE — the foundation the rest is built on.

What affects your BMR

• Body size: bigger bodies burn more at rest.
• Muscle mass: muscle is more metabolically active than fat, so more muscle raises BMR modestly.
• Age: BMR tends to decline with age, partly from muscle loss.
• Sex and genetics: these influence your baseline too.

How to estimate it

The Mifflin-St Jeor equation is a widely used estimate based on your weight, height, age and sex. It’s a solid starting point, though individual BMRs vary around the prediction.

Can you “boost” your BMR?

Not dramatically, despite what supplements claim. The most legitimate lever is building muscle through strength training, which raises BMR somewhat. Crash dieting does the opposite — it can lower BMR by costing you muscle.

Putting it to use

Estimate your BMR, scale up to TDEE with an activity factor, then set your calorie target from there. From that point, your own tracked results — logged easily with Fotocal — refine the estimate into something accurate for you.