Getting a number you can trust
The equation is the easy part. Most of the error comes from two inputs you control.
Pick your activity level for the whole week, not the workout. The multiplier covers your job, your commute, chores and training together. A desk worker who lifts three evenings a week is usually “lightly active”. “Moderately active” means you are on your feet or training hard most days. When two levels both seem right, choose the lower one: that mistake is worth roughly 200 to 300 calories a day, which is the size of a typical deficit.
Treat the result as a three-week experiment. Eat at your target for three weeks and weigh yourself each morning. Compare the average of week one with the average of week three, not single days. If your weight is moving about half a kilogram a week more or less than you expected, adjust by 100 to 150 calories and repeat. That turns an estimate into a number measured on your own body.
The formula behind your target
The calculator works in three steps. First it estimates your basal metabolic rate (BMR) with the Mifflin–St Jeor equation. Then it multiplies by an activity factor to get maintenance calories. Finally it adds or subtracts calories for your goal.
BMR (male) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
BMR (female) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Maintenance = BMR × activity factor (1.2 to 1.9)
Daily target = maintenance + goal adjustmentThe five activity factors are listed with examples on the TDEE calculator page.
| Goal | Calories a day | Typical change a week |
|---|---|---|
| Maintain my weight | maintenance | steady |
| Lose weight slowly | −250 | 0.23 kg (0.5 lb) |
| Lose weight | −500 | 0.45 kg (1.0 lb) |
| Gain weight slowly | +250 | 0.23 kg (0.5 lb) |
| Gain weight | +500 | 0.45 kg (1.0 lb) |
The weekly figures use the common rule of 7,700 calories per kilogram of body weight (3,500 per pound). It is a good guide for the first few weeks and an optimistic one after that, as explained below.
Worked example
A 34-year-old man, 178 cm tall and weighing 82 kg, with an office job and three gym sessions a week (lightly active), who wants to lose weight.
- BMR = 10 × 82 + 6.25 × 178 − 5 × 34 + 5 = 1,768 kcal
- Maintenance = 1,768 × 1.375 = 2,430 kcal
- Target for “Lose weight” = 2,430 − 500 = 1,930 kcal a day
At 1,930 calories he would expect to lose around 0.45 kg (1.0 lb) a week to begin with. Entering these numbers above gives the same result.
Why the scale will not follow the arithmetic
Two things make real weight loss messier than 7,700 calories per kilogram.
The first week is mostly water. Cutting calories, and carbohydrate in particular, empties your glycogen stores, and each gram of glycogen is stored with roughly three grams of water. A quick drop of one to two kilograms in week one is normal and says little about fat.
Your body adapts. As you get lighter you burn less, and your body also trims some of the activity you do without noticing. Researchers at the US National Institute of Diabetes and Digestive and Kidney Diseases built a dynamic model showing that the simple rule overestimates loss over months (Hall et al., 2011). For long plans, their free Body Weight Planner is the better tool. Recalculate here whenever your weight changes by about 5 kg or your routine changes.
The minimum we will show
This calculator will not show a weight-loss target below 1,200 calories a day for women or 1,500 for men. Below those levels it becomes hard to get enough protein, vitamins and minerals, and very low intakes should only be followed under medical supervision. If your chosen goal would go lower, you will see the minimum instead, with a note. The goal table in your result applies the same rule to every row.
These results are general estimates for healthy adults, not medical advice. See the disclaimer for who should check with a professional first.