Most diet advice starts with "eat fewer calories", but fewer than what? The usual answer is your TDEE (total daily energy expenditure): the calories you burn in a normal day. You can estimate it yourself with two steps.
Step 1: Estimate your resting burn (BMR)
The Mifflin-St Jeor equation (1990) is the most widely used one for adults:
- Men:
BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5 - Women:
BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161
Example: a 30-year-old man, 175 cm, 70 kg.
10 x 70 + 6.25 x 175 - 5 x 30 + 5 = 1,649 kcal
The same person as a woman would get 1,483 kcal.
Step 2: Multiply by an activity factor
| Activity | Factor | Example result |
|---|---|---|
| Sedentary, almost no exercise | 1.2 | 1,978 |
| Light, 1-3 days/week | 1.375 | 2,267 |
| Moderate, 3-5 days/week | 1.55 | 2,556 |
| Active, 6-7 days/week | 1.725 | 2,844 |
| Very active, athlete level | 1.9 | 3,133 |
Choose from your whole day, not only your workouts. A desk worker who trains three times a week usually fits "light" better than "moderate".
Turning TDEE into a plan
Roughly 7,700 kcal corresponds to one kilogram of body fat, so a 500 kcal daily deficit is about 0.45 kg per week on paper. In practice weight also moves with water, salt and digestion, so judge your progress on a weekly average, not on single mornings.
- Start with a modest deficit (300-500 kcal) rather than a crash diet.
- Re-check after 2-3 weeks. If the average weekly weight has not moved, adjust by about 100-200 kcal instead of making a big cut.
- Do not rely on a fitness watch's calorie estimate to "eat back" your workouts; consumer devices can be off by a wide margin.
What the estimate cannot do
It is an average for adults, with an individual error of a few hundred calories. It does not apply to children, pregnancy or breastfeeding, and people with medical conditions or on medication should get individual advice before changing their diet.
Disclosure: I built a free calculator that does the two steps above, spo119's daily calorie calculator. Inputs stay in your browser. The formula is simple enough to do by hand if you prefer.
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