TDEE Explained: How to Calculate the Calories You Actually Burn

TDEE stands for Total Daily Energy Expenditure — the total number of calories your body burns in a day, including everything from keeping your heart beating to your evening run. It's the single most useful number in nutrition planning, because every weight goal ultimately comes down to eating above, at, or below it.

BMR vs. TDEE

Your Basal Metabolic Rate (BMR) is the calories your body burns just to stay alive at rest — breathing, circulating blood, maintaining body temperature. It typically accounts for 60–75% of your total daily burn. TDEE takes BMR and adds everything else: digesting food, daily movement, and exercise. FitCalc's calorie calculator estimates BMR first using the Mifflin–St Jeor equation, then multiplies it by an activity factor to get your TDEE.

Why Mifflin–St Jeor?

Older formulas like Harris-Benedict tend to overestimate BMR, particularly for people carrying more body fat. Mifflin–St Jeor, published in 1990 and validated against measured energy expenditure in multiple studies since, is generally considered more accurate for the average adult and is the equation most dietitians default to today. It uses just four inputs — sex, age, weight, and height — which keeps it simple without sacrificing much accuracy for most people.

The activity multiplier is where most people get it wrong

The biggest source of error in any TDEE estimate isn't the BMR formula — it's how honestly you rate your activity level. Someone who works a desk job and goes to the gym three times a week is "lightly active," not "very active," even if the gym sessions feel intense. Overestimating this multiplier is the most common reason people find they aren't losing weight despite "eating at a deficit" — the deficit was never real to begin with.

• Sedentary — desk job, little to no structured exercise
• Light — light exercise or sports 1–3 days a week
• Moderate — moderate exercise 3–5 days a week
• Active — hard exercise 6–7 days a week
• Very active — physical job plus daily training

How to actually use your number

Treat your TDEE as a starting estimate, not a fact. The most reliable way to find your real number is to eat consistently at the calculated target for 2–3 weeks and track your weight trend (not day-to-day fluctuations, which are mostly water). If your weight isn't moving in the expected direction, adjust by 100–200 calories and reassess. This trial-and-adjust approach will always beat any formula, because it accounts for the parts of your metabolism no equation can see — genetics, hormones, sleep quality, and non-exercise movement like fidgeting and walking around during the day.

For weight loss, a deficit of 300–500 calories below TDEE is generally enough to lose fat steadily without the muscle loss and metabolic slowdown that come with more extreme cuts. For weight gain, a surplus of 300–500 calories supports muscle growth without excessive fat gain. Both of these are built into FitCalc's Lose/Maintain/Gain toggle.

This guide is for general education and planning purposes and isn't medical advice. If you have a diagnosed condition affecting your metabolism, or specific medical guidance on calorie intake, follow that guidance over any online calculator.