BMR, RMR, and TDEE: what the calculator can actually estimate

The original equation is REE equals 9.99 times weight in kilograms, plus 6.25 times height in centimetres, minus 4.92 times age in years, plus 166 times sex, minus 161. The study coded male as 1 and female as 0, and the output is kilocalories per day.

The authors also published simplified versions: 10 times weight plus 6.25 times height minus 5 times age, then plus 5 for males or minus 161 for females. Simplifying did not affect predictive value in the study. A calculator should use one published version consistently and show which it uses.

Mifflin and colleagues derived the equation from 498 healthy adults, 247 female and 251 male, aged 19 to 78. The group included 264 normal-weight and 234 obese participants, and resting expenditure was measured with indirect calorimetry.

The model's R-squared value was 0.71, meaning the included variables explained much, but not all, of the measured variation in that sample. The study did not provide constants for people outside its binary sex coding and age range. The calculator should offer both equation results when that limitation makes one choice unclear.

EFSA uses PAL values of 1.4, 1.6, 1.8, and 2.0 for low-active, moderately active, active, and very active sustainable lifestyles when deriving energy reference values. EFSA paired those categories with Henry equations, not Mifflin-St Jeor. This calculator combines the Mifflin estimate with a chosen PAL as a transparent planning shortcut; the hybrid is not presented as a separately validated equation.

FAO emphasizes that the category should reflect work, transport, domestic activity, and leisure activity over a habitual period. A strenuous hour does not define the other 23 hours. If two categories seem plausible, comparing both is more honest than treating the boundary as exact.

For a 35-year-old person weighing 70 kilograms and measuring 170 centimetres, the original female-coded equation gives about 1,429 kcal per day at rest. The male-coded equation gives about 1,595. At PAL 1.6, the corresponding TDEE estimates are about 2,286 and 2,551 kcal per day before display rounding.

The arithmetic is reproducible, but the selected coefficient and PAL visibly move the result. Rounding the displayed expenditure to the nearest 50 kcal keeps attention on the estimate's scale. It does not eliminate uncertainty from body composition, the equation, or the activity description.

The calculator is limited to healthy adults aged 19 to 78 and maintenance expenditure. It does not model pregnancy, breastfeeding, growth, recovery from illness, malnutrition, eating-disorder treatment, elite sport, or a medically prescribed diet. NIDDK applies similar adult, pregnancy, and breastfeeding exclusions to its body-weight planning tool.

Do not subtract a standard deficit or add a standard surplus and call the result safe. Weight-change planning can require a different dynamic model and individual assessment. Stop using the calculator if the numbers feed rigid restriction, compensatory exercise, or anxiety, and seek qualified support.