Every diet plan starts with one number: how many calories you burn in a day. Get that right and losing, maintaining or gaining weight becomes simple arithmetic. It's a two-step calculation — your resting burn (BMR), then your total daily burn (TDEE) once activity is added. This guide walks through both with a worked example, and the free calorie calculator does the maths for you.
Step 1: Basal Metabolic Rate (BMR)
Your BMR is the energy your body uses at complete rest — just breathing, circulating blood and staying alive. The widely used Mifflin-St Jeor formula is:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Step 2: Total Daily Energy Expenditure (TDEE)
Nobody rests all day, so multiply BMR by an activity factor to get TDEE — the calories you actually burn:
- Sedentary (little exercise) → BMR × 1.2
- Lightly active (1–3 days/week) → BMR × 1.375
- Moderately active (3–5 days/week) → BMR × 1.55
- Very active (6–7 days/week) → BMR × 1.725
- Extremely active (hard training/physical job) → BMR × 1.9
Worked example
A 30-year-old woman, 65 kg, 165 cm, moderately active:
| BMR | 10×65 + 6.25×165 − 5×30 − 161 = 1,370 kcal |
| TDEE (×1.55) | 1,370 × 1.55 ≈ 2,124 kcal/day |
She burns roughly 2,124 calories a day — her maintenance level.
Setting calories for your goal
- Lose weight — eat below TDEE. A deficit of ~500 kcal/day targets about 0.5 kg of fat loss a week.
- Maintain — eat at your TDEE.
- Gain — eat above TDEE. A surplus of ~250–500 kcal/day supports lean gain without excess fat.
Since 1 kg of fat is roughly 7,700 kcal, a steady daily deficit is what drives change — crash deficits mostly backfire.
Important caveats
These formulas are estimates, not lab measurements — real metabolism varies with genetics, muscle mass and hormones. Use the number as a starting point, track your weight over 2–3 weeks, and adjust based on what actually happens. For a quick weight-for-height screen, see the BMI calculator. Consult a professional before big dietary changes.
FAQ
What's the difference between BMR and TDEE? BMR is calories burned at rest; TDEE is BMR plus everything you do in a day.
How many calories to lose weight? Eat about 500 below your TDEE for roughly 0.5 kg loss per week.
Which formula is best? Mifflin-St Jeor is currently the most accurate general formula for most people.
Is my data private? Yes — the calculator runs in your browser and stores nothing.