Understanding Your Calorie Needs (TDEE)
Your Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a day, including everything from basic organ function to physical activity. This calculator estimates TDEE in two steps: first calculating your Basal Metabolic Rate (BMR) — the calories you'd burn at complete rest — then multiplying by an activity factor to account for exercise and daily movement.
Eating at your TDEE maintains your current weight. Eating below it creates a calorie deficit for weight loss; eating above it creates a surplus for weight gain. A pound of body fat is roughly equal to 3,500 calories, which is why a 500 calorie/day deficit translates to about 1 pound of weight loss per week.
The Mifflin-St Jeor Formula
Men: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5
Women: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161
TDEE = BMR × Activity Multiplier
This is the formula used by most modern nutrition calculators, including this one, because it's been shown to be more accurate than the older Harris-Benedict equation for most people.
Worked Example
Example
A 28-year-old male, 175cm tall, weighing 70kg, with moderate activity (exercise 3-5 days/week) has a BMR of about 1,665 calories. Multiplying by the moderate activity factor of 1.55 gives a TDEE of roughly 2,581 calories/day to maintain weight. To lose about 1 lb/week, he'd eat around 2,031 calories/day — a 550 calorie deficit.
Tips for Accurate Tracking
- Re-calculate every 10-15 lbs of weight change, since your calorie needs shift as your body weight changes.
- Don't go below 1,200 calories/day (women) or 1,500 (men) without medical supervision — extremely low intakes can slow metabolism and cause nutrient deficiencies.
- Prioritize protein at around 0.7-1g per pound of body weight to preserve muscle mass during a deficit.
- Activity level is often overestimated — if you're unsure, choose the lower activity tier and adjust based on real-world results after 2-3 weeks.
Frequently Asked Questions
How accurate are calorie calculators? ▼
Calorie calculators provide a solid starting estimate, typically within 10-15% of your true TDEE, but individual metabolism varies. The best approach is to use the estimate as a starting point, track your weight for 2-3 weeks, and adjust your intake up or down based on actual results.
Why am I not losing weight at a calorie deficit? ▼
Common reasons include underestimating portion sizes, not accounting for liquid calories, water retention masking fat loss, or an activity level that's set too high in your calculation. Using a food scale for 1-2 weeks often reveals that actual intake is higher than estimated.
How many calories should I eat to gain muscle? ▼
A modest surplus of 250-500 calories above your TDEE, combined with adequate protein (0.8-1g per pound of bodyweight) and resistance training, supports muscle gain while minimizing excess fat gain. Very large surpluses don't speed up muscle building and mostly add fat.
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