If you have ever wondered "how many calories should I eat?", the honest answer is: it depends on how many you burn. That total is your Total Daily Energy Expenditure, or TDEE — the engine number behind every sensible eating plan. Once you know it, deciding how much to eat becomes simple arithmetic.
The two parts of TDEE
Your daily calorie burn is built from two pieces. The first and largest is your Basal Metabolic Rate (BMR) — the energy your body spends just keeping you alive: breathing, circulating blood, maintaining temperature and repairing cells. For most people BMR accounts for 60–70% of all the calories they burn, even on a lazy day.
The second piece is everything you do: walking, working, exercising, fidgeting, and even digesting food. To turn BMR into TDEE, we multiply it by an activity factor:
Estimating BMR: the Mifflin-St Jeor equation
The most widely used and best-validated formula for BMR is the Mifflin-St Jeor equation. It uses your weight, height, age and sex:
where s is +5 for men and −161 for women. For example, a 30-year-old man weighing 80 kg at 180 cm has a BMR of (10×80) + (6.25×180) − (5×30) + 5 = 800 + 1125 − 150 + 5 = 1,780 calories a day at complete rest.
The activity multipliers
Multiply BMR by the factor that best matches your typical week. Be honest — most people overestimate how active they are, which is the single biggest source of error.
| Activity level | Factor | Example for BMR 1,780 |
|---|---|---|
| Sedentary (little or no exercise) | 1.2 | 2,136 |
| Lightly active (1–3 days/week) | 1.375 | 2,448 |
| Moderately active (3–5 days/week) | 1.55 | 2,759 |
| Very active (6–7 days/week) | 1.725 | 3,071 |
| Extra active (hard training or physical job) | 1.9 | 3,382 |
So the same person could need anywhere from about 2,100 to 3,400 calories a day depending purely on how much they move. That range is exactly why a single "2,000 calories a day" guideline fits almost no one precisely.
Using TDEE to hit your goal
Your TDEE is your maintenance level — eat that much and your weight holds steady. To change weight, you shift around it:
- To lose fat: eat below TDEE. A pound of fat stores roughly 3,500 calories, so a daily deficit of about 500 calories yields close to 1 lb (0.45 kg) of loss per week. A 250-calorie deficit is slower but easier to live with.
- To maintain: eat at TDEE. Useful for athletes holding weight or anyone happy where they are.
- To gain muscle: eat above TDEE — a modest surplus of 250–500 calories supports muscle growth without excessive fat gain, especially combined with resistance training.
A common mistake is cutting too hard. Very large deficits are difficult to sustain, can cost you muscle as well as fat, and often backfire when hunger wins. Smaller, steady changes almost always beat dramatic ones.
Why the number is an estimate, not a law
Formulas like Mifflin-St Jeor are accurate on average but can be off for any individual. Body composition matters — muscle burns more at rest than fat — as do genetics, hormones, sleep and how precisely you track food. Treat your calculated TDEE as a well-informed starting point. Eat at it for two to three weeks, watch what your weight actually does, and adjust by 100–200 calories if reality disagrees with the maths.
TDEE and BMI together
BMI tells you where your weight sits relative to your height; TDEE tells you how to move it. They pair naturally: check your BMI to see whether a change makes sense, then use TDEE to plan the calories to get there. Remember that BMI can't tell muscle from fat, so someone building muscle in a calorie surplus may see BMI rise while body composition improves.
Try it yourself
The free TDEE calculator runs the Mifflin-St Jeor equation and the activity multipliers for you, and shows target calories for losing, maintaining and gaining weight. Pair it with the BMI calculator to see the full picture in metric or imperial units.
Frequently asked questions
- What is TDEE?
- Total Daily Energy Expenditure — the total calories your body burns in a day, combining your resting metabolism with the energy used for activity, exercise and digestion.
- What is the difference between BMR and TDEE?
- BMR is the calories you'd burn at complete rest. TDEE is BMR multiplied by an activity factor (1.2 to 1.9), so it's always higher and reflects how much you actually move.
- How many calories should I eat to lose weight?
- Below your TDEE. A 500-calorie daily deficit yields about 1 lb of fat loss per week; a 250-calorie deficit is gentler. Avoid very low intakes without professional guidance.
- How accurate is a TDEE calculator?
- Usually within about 10% for most people. The Mifflin-St Jeor equation is well validated, but metabolism and how honestly you rate activity affect it. Use it as a starting point and adjust by results.
This guide is for educational purposes only and does not provide medical or dietary advice. Calorie needs vary between individuals — consult a qualified professional before making significant changes to your diet.