Health
Calorie Calculator
The resting figure is a published equation. The activity multiplier is a convention — the page keeps them apart.
The formula
BMR (men) = 10 × kg + 6.25 × cm − 5 × age + 5
BMR (women) = 10 × kg + 6.25 × cm − 5 × age − 161
daily energy = BMR × activity multiplier
Worked example
A 35-year-old man, 175 cm, 74 kg, moderately active
- 10 × 74 = 740
- 6.25 × 175 = 1,093.75
- 740 + 1,093.75 − 175 + 5 = 1,663.75 kcal at rest
- 1,664 × 1.55 = 2,579 kcal a day
Where this goes wrong
Treating a regression on 498 people as your own metabolism
Mifflin–St Jeor was fitted to 498 healthy adults and reports R² = 0.71 — it explains 71% of the variation between individuals, which means close to a third of it is something else entirely. For a resting figure near 1,664 kcal, the honest spread is roughly ±250 kcal before the activity multiplier is even applied, and that multiplier is a convention with no comparable evidence behind it. The output is a starting estimate to adjust against what actually happens to your weight over a few weeks, not a budget to obey to the kilocalorie.
Questions
- What is BMR and how is it different from daily calories?
- Basal or resting metabolic rate is what your body uses doing nothing at all — breathing, circulating, maintaining temperature. Daily energy is that figure multiplied by an activity factor. The first is measured science; the second is an educated convention, which is why this page shows them as separate numbers.
- Which equation does this use, and why?
- Mifflin–St Jeor, published in the American Journal of Clinical Nutrition in 1990 from indirect calorimetry on 498 healthy adults. It replaced the older Harris–Benedict equation, derived in 1919 from a much smaller and less representative sample, and it remains the best-validated predictor for healthy adults.
- Why does the equation only offer two options for sex?
- Because that is what the 1990 study measured: it fitted two constants, +5 and −161, to male and female subjects. This page reports the equation as published rather than extrapolating beyond its data. If neither constant describes you, the honest reading is that this equation was not derived for your case.
- How accurate is it for me personally?
- Approximately, and the page tells you how approximately. R² = 0.71 means the four inputs account for about 71% of the differences between people; body composition, thyroid function, genetics and measurement error account for the rest. Use it as a starting point and correct it against your own results.