How to calculate your daily calories

Daily calorie expenditure — TDEE, for Total Daily Energy Expenditure — is how much energy your body burns in 24 hours. It is the number that decides whether you lose, maintain or gain weight, and most of it has nothing to do with exercise.

The four components

• Basal metabolic rate (BMR): what your body spends at complete rest just to keep running — heart, breathing, brain, temperature. It is the largest slice, typically 60% to 70% of the total.
• Thermic effect of food: the energy spent digesting and absorbing what you eat, around 10% of the total. Protein costs considerably more to process than fat or carbohydrate.
• Non-exercise activity (NEAT): walking, taking stairs, gesturing, standing, fidgeting. This is the most variable component between people — it can differ by hundreds of calories a day.
• Exercise: the gym and the run. For most recreational exercisers, it is the smallest slice.

The standard formula: Mifflin-St Jeor

Men: BMR = 4.536 × weight(lb) + 15.88 × height(in) − 5 × age + 5

Women: BMR = 4.536 × weight(lb) + 15.88 × height(in) − 5 × age − 161

Then multiply BMR by an activity factor:

Routine	Factor
Sedentary (desk job, no training)	1.2
Lightly active (1 to 3 days a week)	1.375
Moderately active (3 to 5 days)	1.55
Very active (6 to 7 days)	1.725
Extremely active (physical job plus training)	1.9

Worked example

A woman at 150 lb, 5'5" (65 in), 32 years old, training three times a week:

1. 4.536 × 150 = 680.4
2. 15.88 × 65 = 1,032.2
3. 5 × 32 = 160
4. BMR = 680.4 + 1,032.2 − 160 − 161 = 1,392 kcal
5. TDEE = 1,392 × 1.375 = 1,914 kcal a day

Look at the size of the BMR: 1,392 of those 1,914 calories are spent without moving. That is the body simply operating.

Training burns less than you think

Here is the counter-intuitive part. An hour's run at 5 mph, for someone weighing 176 lb, burns roughly 660 kcal — and that is a long session most people do not do daily. A muffin and a latte can put half of it back in three minutes.

Hence the line that summarises the literature: you cannot out-train a bad diet. Not because exercise is useless — it is decisive for cardiovascular health, lean mass and mood — but because, as a tool for creating a calorie deficit, it is slow compared to food.

There is a second effect worth knowing: the body compensates. In many people, a hard training day spontaneously reduces NEAT across the rest of the day. You train more and move less without noticing.

What the formula misses

• Body composition. Mifflin-St Jeor uses only weight, height, age and sex. Two people at the same weight with very different body-fat percentages have different BMRs, because muscle costs more energy at rest.
• Individual variation. BMR equations typically land within about 10% either way of a measurement by indirect calorimetry. For someone with a 2,000 kcal TDEE, that is a 200-calorie band.
• Adaptation. Through a long period of restriction, expenditure falls — partly from lost mass, partly from reduced NEAT and metabolic efficiency.

Treat the formula as a starting point, not a fact. The real calibration comes from testing: hold intake steady for two to three weeks, track the weekly average weight, and adjust.

Frequently asked questions

What deficit should I use to lose weight? A deficit of 15% to 20% of TDEE is the most sustainable range, which usually works out to 300 to 500 kcal a day. Aggressive deficits accelerate lean-mass loss and adherence collapses.

Should I add my workout calories on top? Only if you chose the 1.2 (sedentary) factor. Factors of 1.375 and above already include exercise — adding it again double-counts, and it is one of the most common errors among app users.

Why does my watch show such a different number? Watches and treadmills frequently overestimate burn, sometimes by 20% to 30%, because they infer from heart rate and steps without knowing your actual efficiency. Use them for trend, not accounting.

Do men burn more than women? On average yes, and the formula encodes that in the constant (+5 versus −161). The main driver is the average difference in lean mass, not sex itself.

Sources: Mifflin MD, St Jeor ST et al., A new predictive equation for resting energy expenditure in healthy individuals (American Journal of Clinical Nutrition, 1990); Compendium of Physical Activities (Ainsworth et al.) for MET values. Informational content — it does not replace advice from a dietitian or physician.