How the calories are worked out
1. Basal metabolic rate (BMR) by the Mifflin-St Jeor equation (1990): men 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; women 10 × weight + 6.25 × height − 5 × age − 161. It is what your body burns at complete rest.
2. Maintenance calories (TDEE) = BMR × an activity factor: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 high, 1.9 very high. These are widely used approximate factors, not exact values for any one person.
Illustrative example: a 35-year-old woman, 165 cm, 70 kg: 700 + 1,031.25 − 175 − 161 = 1,395 kcal BMR. At moderate activity: 1,395.25 × 1.55 = 2,163 kcal to maintain her weight. With a gentle cut of about 500: 1,663 kcal.
Gentle goals and the minimum
- Lose slowly: the calculator subtracts about 500 kcal from maintenance. The NHS says a safe rate is about 0.5 to 1 kg a week.
- Gain slowly: it adds 250 kcal. That is our own cautious choice, not a figure from a medical source.
- A floor of 1,200 kcal: the calculator never suggests less, because the NHS says plans under 800 or 1,200 kcal need a dietitian’s supervision and are not suitable for everyone. If the cut reaches this floor, the calculator tells you.
- It does not suggest losing weight if your BMI is below 18.5.
Common mistakes
- Picking a higher activity level than the real one: a desk job with a little exercise is usually “light”, not “high”.
- Treating the number as exact. It is an estimate, and your body may differ, so watch your weight for a few weeks before adjusting.
- Cutting calories too far for faster results.
For medical conditions or a special diet, see a doctor. MyClinic (Sehaty) lets patients search for a doctor by speciality and location and book without a phone call, and the medical file keeps their health history.
How to book a doctor online in Egypt · See MyClinic · Request a demo
Sources
- Mifflin et al., Am J Clin Nutr 1990;51:241-7 (the BMR equation)
- NHS: obesity treatment (0.5 to 1 kg a week; plans under 800 or 1,200 kcal with a dietitian)
- The activity factors 1.2 to 1.9 are in wide use and are attributed to McArdle’s Exercise Physiology; we could not confirm them from a primary source, so treat them as approximate.
Questions
How do I calculate my BMR?
Use the Mifflin-St Jeor equation: 10 × weight + 6.25 × height − 5 × age, then add 5 for men or subtract 161 for women.
How many calories do I need a day?
The calculator multiplies your BMR by your activity factor. A moderately active woman with a BMR of 1,395 needs about 2,163 kcal to keep her weight (illustrative).
How many calories should I cut to lose weight?
The calculator suggests about 500 fewer, with a floor of 1,200. The NHS points to 0.5 to 1 kg a week.
Why does it never suggest under 1,200 kcal?
The NHS says plans below that need a dietitian’s supervision and are not for everyone. If you need a lower plan, ask your doctor.
Is the number accurate?
It is an estimate. Your body may differ, so track your weight for a few weeks and adjust.
Can pregnant or breastfeeding women or under-18s use it?
No. It is for adults aged 18 to 80. For pregnancy, breastfeeding or chronic conditions, ask your doctor.
Read the guide
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