Estimate your daily calorie needs based on the Mifflin-St Jeor equation and activity level.
Men: BMR = 10w + 6.25h - 5a + 5
Women: BMR = 10w + 6.25h - 5a - 161
TDEE = BMR × activity multiplier (sedentary 1.2 to very active 1.9). This is a widely used estimate for weight management and nutrition planning.
TDEE (total daily energy expenditure) is your BMR multiplied by an activity factor, and picking the right factor matters more than most people expect — one level off in either direction can shift your daily calorie target by roughly 300-500 calories. The standard bands are sedentary ×1.2 (little to no exercise, desk job), lightly active ×1.375 (light exercise 1-3 days/week), moderately active ×1.55 (moderate exercise 3-5 days/week), very active ×1.725 (hard exercise 6-7 days/week), and extra active ×1.9 (very hard exercise plus a physical job or twice-daily training).
The most common mistake isn't the formula, it's the input: most people genuinely overestimate their own activity level, counting a gym session as "very active" even though the other 22 hours of the day are spent sitting. If you're unsure which band fits, start one level lower than your instinct — a sedentary office worker who lifts weights three times a week is usually "lightly active," not "moderately active," because the multiplier is meant to reflect your whole day's movement, not just the workout itself. Once you have a TDEE figure, a calorie deficit for fat loss or surplus for muscle gain is calculated relative to that number, not relative to BMR alone.
BMR is the energy your body burns at complete rest — no activity at all. TDEE takes that BMR and multiplies it by an activity factor (1.2 to 1.9) to account for daily movement, exercise and digestion, giving you the realistic total number of calories you burn in a full day.
Most people overestimate their own activity level. If you're unsure between two bands, choose the lower one — a desk-job worker who exercises a few times a week is usually "lightly active" (×1.375), not "moderately active" (×1.55), since the multiplier reflects your entire day, not just the gym session.
A lot — moving one band changes your daily calorie estimate by roughly 300 to 500 calories, which over weeks can be the difference between a real deficit or surplus and simply maintaining weight. It's worth re-checking your activity level honestly rather than defaulting to an optimistic guess.
TDEE is your maintenance calorie estimate — eating at it keeps weight roughly stable. For fat loss you'd typically eat a moderate deficit below TDEE, and for muscle gain a modest surplus above it; TDEE itself is the reference point both plans are built from, not a fixed daily rule.