How Many Calories Do You Actually Need?
Calorie calculators give different answers because they use different formulas, different activity multipliers, and because individual metabolism genuinely varies. Understanding what these tools are calculating — and their limits — helps you use the number more intelligently.
BMR — Your Baseline
Basal Metabolic Rate is the number of calories your body burns at complete rest — just to keep organs functioning, maintain body temperature and stay alive. It accounts for roughly 60-70% of total daily calorie expenditure for most people.
BMR is estimated using formulas based on height, weight, age and sex. The most widely validated is the Mifflin-St Jeor equation (1990):
- Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5
- Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161
An alternative, the Harris-Benedict equation (1918, revised 1984), is still widely used but slightly less accurate on average for modern populations.
TDEE — Your Real Number
Total Daily Energy Expenditure is BMR multiplied by an activity factor. This is the number you actually need — calories burned across the full day including movement, exercise and the thermic effect of food (calories burned digesting food).
Standard activity multipliers: Sedentary (desk job, no exercise) ×1.2 / Light activity ×1.375 / Moderate activity ×1.55 / Very active ×1.725 / Extremely active ×1.9.
Most people significantly overestimate their activity level. "Moderate activity" means deliberately exercising 3-5 days per week — not just walking to work. If unsure, start with the multiplier below what feels right.
Why Different Calculators Give Different Numbers
Different formulas, different activity multiplier scales, and different assumptions. A 10-15% variation between calculators for the same inputs is normal. None of them know your actual metabolism — they give a statistically likely estimate for someone with your characteristics.
How to Use the Number
Treat your calculated TDEE as a starting point, not a precise target. Track your actual food intake against this number for 2-3 weeks. If your weight is stable, your real TDEE is close to the calculated figure. If you are gaining or losing unexpectedly, adjust accordingly.
For weight loss, a deficit of 300-500 calories per day produces steady, sustainable loss (roughly 0.3-0.5kg per week). Larger deficits are harder to sustain and risk muscle loss.
Individual Variation
Two people with identical stats can have metabolisms that differ by 200-300 calories per day due to genetics, gut microbiome, hormones and other factors. This is why "eating 1,200 calories and not losing weight" is a real experience — their TDEE may simply be lower than expected. The formula is a useful estimate, not a biological law.