BMR and TDEE

BMR (Basal Metabolic Rate) is the amount of energy your body burns at complete rest — just to keep you alive. Breathing, your heartbeat, cell repair and brain function all consume calories even while you sleep, and that baseline is your BMR. TDEE (Total Daily Energy Expenditure) is the bigger, more useful number: your BMR multiplied by an activity factor, representing your real daily calorie burn once movement and exercise are included.

How the numbers connect

A typical chain looks like this:

• BMR — the resting baseline described above.
• Activity factor — a multiplier from roughly 1.2 (sedentary) to 1.9 (very active or highly physical job).
• TDEE = BMR × activity factor — your total maintenance energy.

So a person with a BMR of 1,500 calories and a moderately active lifestyle (factor ~1.5) would have a TDEE of around 2,250 calories.

Why TDEE matters for weight

Your weight changes based on how your calorie intake compares to your TDEE:

• Eat below TDEE — a deficit of about 500 calories a day typically leads to roughly half a kilogram of fat loss per week.
• Eat near TDEE — you maintain your current weight.
• Eat above TDEE — you gain.

These are estimates, not precise numbers. Individual metabolism, muscle mass, hormones and daily movement all shift the true figure.

Doing the weight-math correctly

A healthy change targets a moderate deficit or surplus rather than extreme jumps, since the body often adapts. Importantly, as you drop weight your BMR falls slightly (a smaller body needs less energy), so your maintenance number moves with you — recalculating as you progress keeps the plan on track.

How BMR is estimated

The most accurate common bedside formula is Mifflin-St Jeor (1990), which uses weight, height and age:

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

An earlier alternative, the Harris-Benedict equation (1919), is still used but tends to overestimate modern needs because it was derived from a smaller, historically heavier sample. The Mifflin-St Jeor revision was developed in part to correct that drift.

Get your resting number with the BMR Calculator and your realistic daily target with the TDEE Calculator.