Your body burns calories around the clock — even while you sleep. Two numbers capture most of that story, and mixing them up is the single most common calorie-counting mistake. BMR vs TDEE: BMR (basal metabolic rate) is what you would burn lying in bed doing nothing all day, while TDEE (total daily energy expenditure) adds everything you actually do on top of it. This guide explains both, the Mifflin-St Jeor equation behind our free calorie calculator, and a worked example you can verify by hand.
Quick note: the numbers below are estimates only, not medical advice. If you have a medical condition, are pregnant, or are planning a large calorie deficit, talk to a doctor or registered dietitian first.
What is BMR?
Your basal metabolic rate is the energy your body needs to keep you alive at complete rest — breathing, circulation, brain function, cell repair. For most people it accounts for roughly 60–70% of all calories burned in a day. BMR depends mainly on your weight, height, age and sex: bigger bodies burn more, and BMR slowly declines with age as muscle mass drops.
What is TDEE?
Total daily energy expenditure is BMR plus everything else: exercise, walking, standing, fidgeting (scientists call this NEAT — non-exercise activity thermogenesis), and even the energy cost of digesting food. TDEE is the number that actually matters for weight goals: eat consistently below it and you lose weight; eat above it and you gain. BMR is the engine idling — TDEE is the engine driving your real day.
The Mifflin-St Jeor equation
The Mifflin-St Jeor equation is one of the most widely validated formulas for estimating BMR in typical adults, and it is what our calorie calculator uses:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
The formula needs metric units, so convert first: pounds ÷ 2.205 = kilograms, inches × 2.54 = centimeters.
How to calculate your TDEE in 4 steps
- Convert your weight and height to metric. For example, 180 lbs ÷ 2.205 = 81.65 kg, and 70 inches × 2.54 = 177.8 cm.
- Plug the numbers into Mifflin-St Jeor. This gives your BMR — your at-rest burn.
- Pick an activity multiplier that honestly matches your week: 1.2 (sedentary, desk job, little exercise), 1.375 (lightly active, 1–3 workouts/week), 1.55 (moderately active, 3–5 workouts/week), 1.725 (very active, hard exercise most days), 1.9 (extremely active, physical job or two-a-days).
- Multiply BMR × activity multiplier. The result is your TDEE — roughly how many calories you burn per day.
Worked example: 30-year-old man, 5'10", 180 lbs, moderately active
- Convert: 180 lbs = 81.65 kg; 70 in = 177.8 cm
- BMR = 10 × 81.65 + 6.25 × 177.8 − 5 × 30 + 5 = 816.5 + 1111.25 − 150 + 5 = 1,783 cal/day
- TDEE = 1,783 × 1.55 (moderately active) = 2,763 cal/day
So this person burns roughly 2,763 calories per day. Eating about 2,263/day (a 500-calorie deficit) would predict roughly a pound of fat loss per week; eating about 3,263/day would support gradual weight gain. Run your own numbers in seconds with the free calorie calculator.
Common mistakes
- Eating at or below your BMR for long stretches. BMR is the floor your organs need — chronic deficits below it bring fatigue, muscle loss and stalled progress.
- Confusing BMR with TDEE. Eating 1,783 calories when your TDEE is 2,763 is nearly a 1,000-calorie deficit — far more aggressive than most people intend.
- Overestimating activity. Most people pick a level too high; when in doubt, choose one level lower or average two adjacent multipliers.
- Never recalculating. A lighter body burns fewer calories — rerun the numbers every 5–10 lbs of change.
- Forgetting liquid calories and cooking oils. Drinks, dressings and the oil in the pan can add hundreds of uncounted calories.
- Treating the estimate as a prescription. It is a starting point: track for 2–3 weeks, watch the scale and energy, then adjust.
Curious how your weight stacks up against healthy ranges too? Check your numbers with our BMI calculator and read the BMI guide for context — and if you need your exact age for the formula, our age calculator has you covered.