What this calorie calculator does
Enter sex, age, height and weight, pick your activity factor, and the calculator shows your basal metabolic rate using the Mifflin-St Jeor equation, your total daily energy and your target calories for maintaining, losing or gaining — plus a rough macro split. Metric or imperial, and everything is computed locally in your browser.
Which formula is behind it?
The Mifflin-St Jeor equation from the American Journal of Clinical Nutrition (Mifflin MD, St Jeor ST et al., 1990;51(2):241–247, derived from 498 healthy adults aged 19 to 78):
| Formula (kcal/day) | |
|---|---|
| Men | 10 × kg + 6.25 × cm − 5 × age + 5 |
| Women | 10 × kg + 6.25 × cm − 5 × age − 161 |
A 30-year-old man at 80 kg and 180 cm gets 800 + 1125 − 150 + 5 = 1780 kcal basal rate. You can switch to the Harris-Benedict revision by Roza and Shizgal (1984) to compare; for the same person it lands at roughly 1854 kcal.
Why Mifflin-St Jeor rather than Harris-Benedict?
Because it holds up best in direct comparison. A systematic review by Frankenfield and colleagues in the Journal of the American Dietetic Association (2005;105(5):775–789) compared the common estimating equations against resting metabolic rates measured by indirect calorimetry: Mifflin-St Jeor landed within 10 percent of the measured value more often than Harris-Benedict, Owen or WHO/FAO/UNU, in both non-obese and obese adults, and had the narrowest error range. The same review notes that older adults and ethnic minorities were underrepresented in the underlying studies.
Which PAL value should I choose?
The PAL value (physical activity level) scales your basal rate to the whole day: total daily energy = basal rate × PAL.
| PAL | Who it fits |
|---|---|
| 1.2 | Desk job or working from home, little exercise, mostly seated |
| 1.375 | Seated work plus 1–3 easy sessions a week |
| 1.55 | Standing or walking job, or 3–5 sessions a week |
| 1.725 | Physical job, or 6–7 sessions a week |
| 1.9 | Hard physical work plus daily training |
If in doubt, take the lower value. At a basal rate of 1780 kcal, the gap between 1.55 and 1.725 is already about 310 kcal a day — enough to quietly swallow a planned deficit.
How big should a deficit be?
The usual range is 10 to 20 percent below total daily energy: slow enough to live with, fast enough to notice. The calculator applies exactly the percentage you set and shows the difference in kilocalories alongside.
The macro split is a rough orientation, not a prescription. It uses the Atwater factors: 4 kcal per gram of protein, 4 kcal per gram of carbohydrate, 9 kcal per gram of fat.
Honest limits
- The result is an estimate for healthy adults, not a measurement. At identical height, weight and age people differ by several hundred kilocalories — the equation knows nothing about muscle mass or thyroid function.
- Children and teenagers, pregnancy and breastfeeding, illness and competitive sport all need different reference values. This calculator is not built for them.
- The PAL factor is the largest source of error, because it rests on self-assessment.
- More reliable than any formula is your own data: hold the target for four weeks, watch the scale, then adjust.
Privacy
Age, height, weight and goal stay on your device. The calculation runs entirely in the browser and your entries are kept in local storage only, so the tool remembers them next time.
This calculator is general information and not medical or dietary advice. If you have a health condition, are significantly over- or underweight, or are planning a major change in how you eat, please talk to a qualified professional.