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Maintaining, losing or gaining weight all come down to one number: your daily maintenance calories — the energy you need to keep your current weight with no change. Eat below it and you lose, above it and you gain; that's the whole logic of calorie counting.
Enter your age, height, weight, sex and activity level, and your basal metabolism, daily maintenance calories and loss/gain targets are calculated together.
How is it calculated?
A two-layer calculation
1. Basal metabolic rate (BMR): the energy burned just to stay alive — breathing, circulation, organ function — with no movement. The tool uses the widely accepted Mifflin-St Jeor formula:
- Men: 10 × kg + 6.25 × cm − 5 × age + 5
- Women: 10 × kg + 6.25 × cm − 5 × age − 161
2. Activity multiplier (PAL): BMR is multiplied by how active you are.
| Activity level | Multiplier |
|---|---|
| Sedentary (desk job) | 1.20 |
| Lightly active (1-3 days/week) | 1.375 |
| Moderately active (3-5 days) | 1.55 |
| Very active (6-7 days) | 1.725 |
| Extremely active (hard job/2× training) | 1.90 |
Targets by goal
- Maintain: eat at your maintenance calories.
- Lose: aim for a ~300-500 kcal deficit per day; ~0.3-0.5 kg per week is a healthy pace. Extreme deficits (1000+ kcal/day) cost muscle and aren't sustainable.
- Gain: aim for a ~300-500 kcal surplus; pair with training to build muscle.
Calorie quality matters too: within the same calories, protein is decisive for satiety and preserving muscle. For a macro split use a protein calculator and a macro calculator.
Worked example
A 30-year-old man, 180 cm, 82 kg: BMR = 10×82 + 6.25×180 − 5×30 + 5 = 1,800 kcal. If moderately active (3-5 days of exercise a week) his maintenance is 1,800 × 1.55 = 2,790 kcal. To lose weight he'd target roughly a 300 kcal deficit at 2,490 kcal, losing about half a kilo a week. If sedentary, his maintenance would drop to 1,800 × 1.20 = 2,160 kcal — showing that activity alone accounts for a 630 kcal difference per day.
FAQ
How are daily calorie needs calculated?+
First the basal metabolic rate (BMR) is found with the Mifflin-St Jeor formula, then multiplied by an activity factor (1.2–1.9). The result is the calories needed to maintain your weight.
How many calories should I eat to lose weight?+
About 300-500 kcal below your maintenance per day. That gives a healthy, sustainable loss of roughly 0.3-0.5 kg per week. Very large deficits cost muscle mass.
Is BMR the same as daily calorie needs?+
No. BMR is the energy burned at complete rest; daily needs are BMR multiplied by an activity factor to reflect your real life. Daily needs are always higher than BMR.
How do I choose my activity level?+
Consider how many days and how intensely you move: a desk job with little walking is "sedentary," 3-5 training days is "moderately active." If unsure, choosing one level lower is safer.
Why do calorie needs differ between men and women?+
The formula adds +5 for men and −161 for women, reflecting average differences in muscle mass and body composition. At the same height, weight and age, a man's needs are somewhat higher.
How much should I trust the calculated figure?+
Formulas give a good starting estimate, but metabolism varies. Follow the figure for 2-3 weeks and track your weight; if the change differs from expected, adjust by 100-200 kcal.