Mifflin–St Jeor at rest
Mifflin–St Jeor estimates resting energy from weight, height, age, and a sex constant. For a 30-year-old male at 75 kg and 175 cm, 10 × 75 + 6.25 × 175 − 5 × 30 + 5 equals about 1,699 kcal per day. It represents an average day at rest, not food advice.
Rest is not a normal day
BMR excludes walking, work, exercise, digestion, and deliberate training. It is therefore lower than the energy used on a normal day. Multiplying it by an activity estimate can be useful for a rough planning scenario, but the multiplier is an assumption rather than a measurement from this calculator.
Why measured needs differ
Laboratory indirect calorimetry measures oxygen and carbon-dioxide exchange under controlled conditions; this equation does not. Body composition, illness, fever, thyroid status, medicines, recent weight change, and measurement error can all make an individual result differ from the equation.
An estimate is not a prescription
Entering 75.0 kg and 175.0 cm may produce a whole-calorie answer, but that does not make the estimate accurate to one calorie. Use the figure as a starting range and compare it with observed intake, weight trend, activity, and professional guidance when nutrition planning has health consequences.
Keep the calculation reproducible
Weight and age assumptions should be updated when circumstances change. A saved calculation should include the equation name and date so it is not mistaken later for a measured metabolic test.
Check the arithmetic in context
A useful reality check is to distinguish the calculation from an observed energy balance. If a stable intake and weight trend over several weeks disagree with the estimate, that observation may be more relevant for planning than repeatedly changing a formula input. Do not try to make the answer match a desired calorie number by altering age, height, or sex constants. Those are description fields, not adjustable levers.
The equation uses a binary sex constant because that is how it was constructed; it does not capture every person's physiology or identity. When clinical nutrition, hormone treatment, or unusual metabolic symptoms are relevant, use a care team's method rather than selecting a constant merely to obtain a preferred output.
It is informational only and is not medical or professional advice.