How we calculate

We want every number on this site to be checkable. Here is where the targets, food data and tips come from — and what the calculator doesn’t account for.

Daily calorie needs

Resting energy expenditure is calculated with the Mifflin–St Jeor equation (Mifflin et al., 1990). It was derived from measurements in 498 healthy people aged 19–78; in the same study the older Harris–Benedict equations overestimated needs by 5% on average.

Men:   10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) + 5
Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) − 161

We then multiply by an activity factor — from 1.2 (sedentary) to 1.9 (physical work or training twice a day) — and adjust for your goal: −15% to lose weight, +10% to gain.

Protein, fat and carbs

Protein is based on body weight: 0.83 g per kilogram, enough for 97.5% of healthy adults (Rand et al., 2003); 1.2 g/kg from age 65, the upper end of recommendations for older people (Bauer et al., 2013); and 1.6 g/kg to gain weight, since more protein adds no further muscle gain with resistance training (Morton et al., 2018). Fat is 30% of calories (25% to gain weight), and carbs make up the rest. One gram of protein or carbs provides 4 kcal, fat 9 kcal. More in How much protein do you really need.

• saturated fat — no more than 10% of calories (WHO);
• omega-6 — about 4% of calories, omega-3 — 0.5% (EFSA, the European Food Safety Authority);
• fiber — 14 g per 1,000 kcal;
• free sugars — no more than 10% of calories (WHO). WHO counts sugar added to food plus honey, syrups and juices, but not sugar in whole fruit, vegetables and milk. The USDA database doesn’t list free sugars, so we estimate the share for each sweet food: all of the sugar in sugar, honey, juices and confectionery; for yogurt, ice cream or ketchup, total sugar minus the natural sugar of an unsweetened counterpart.

Vitamins and minerals

Targets are Recommended Dietary Allowances (RDA) or Adequate Intakes (AI) for adults from the NIH Office of Dietary Supplements and the US National Academies; they depend on sex and age. Pregnancy, breastfeeding, childhood and medical conditions aren’t covered — targets differ there.

Body mass index

BMI is weight (kg) divided by height (m) squared. We use the WHO classification (WHO, 2000): normal weight is a BMI of 18.5 to 24.9, overweight starts at 25 and obesity at 30 (three classes). The normal weight range for your height is the weight at which BMI falls within 18.5–24.9. For Asian populations, risks rise at lower BMI values, but WHO didn’t propose a different cut-off and advised keeping the international classification (WHO, 2004).

BMI is a rough estimate, not a diagnosis. In a survey of 13,601 adults from NHANES III, a BMI of 30 or more was rarely wrong when it said “obese” (specificity 95% in men and 99% in women) but missed most cases: it detected excess body fat in only 36% of men and 49% of women. In the intermediate range of 25–29.9 it couldn’t tell fat from lean mass, and accuracy fell with age (Romero-Corral et al., 2008). That’s why we show it as a reference number.

Water

The target is the Adequate Intake of total water from the EFSA opinion: 2.0 L a day for women and 2.5 L for men. It includes both drinks and moisture from food (about 20% on average) and is set for a temperate climate and moderate physical activity. It doesn’t depend on body weight, and we don’t use formulas like “30 ml per kg” — they aren’t among the sources we rely on.

It’s a guide, not any one person’s requirement. In a study of water turnover in 5,604 people from 23 countries, it depended on age, body size, physical activity, pregnancy, climate and socioeconomic factors (Yamada et al., 2022), and there is still no widely accepted water requirement for different groups (Armstrong, Johnson, 2018). The familiar “eight glasses a day” has no scientific backing: this review found no studies in its support (Valtin, 2002). More water is needed during hard work and exercise, especially in the heat.

Food and dish data

Food composition comes from USDA FoodData Central (Foundation Foods and SR Legacy). Each food is pinned to a specific database record, described and linked on its food page. Ukrainian dishes are calculated from recipes: the raw weight of each ingredient with cooking taken into account, divided by the weight of the finished dish.

How cooking is handled

Grains absorb water when boiled and meat loses it when fried, so 100 g cooked has different calories from 100 g raw. For grains and legumes the yield comes from raw–boiled pairs in the USDA database (buckwheat ×3.76, pasta ×2.35); for other foods it is an average for the category.

Some vitamins break down with heat or leach into the water. For grains and legumes we take these losses from the same USDA raw–boiled pairs, separately for each vitamin and mineral: cooked buckwheat keeps about 68% of its vitamin B1 and 87% of its magnesium. The raw and cooked samples differ, so sometimes the cooked one shows more of a nutrient than the raw had; we then treat it as fully retained. For other foods and cooking methods the losses are approximate percentages for nutrient groups (vitamin C, B vitamins, fat-soluble vitamins, minerals), not lab data for each food.

Food-pairing tips

Every tip — tea and iron, vitamin C, calcium, fat and carotenoids — rests on studies we checked against the original on PubMed; the link is under each tip. How much iron or calcium you actually absorb depends heavily on the whole meal, so we don’t compute “absorbed milligrams”; we show what helps and what hinders. More in the articles.

Limitations

• The formulas estimate needs for an average person; your actual energy use can differ noticeably. The best guide is how your weight changes over a few weeks.
• The calculator doesn’t replace advice from a doctor or dietitian, especially with medical conditions, in pregnancy and for children.
• Your profile, diary and custom foods are stored only in your browser — we don’t see or share them.