Basal metabolic rate (BMR) is an estimate of the energy the body would use at rest under standardized conditions. It is not the number of calories you necessarily burn in an ordinary day because normal movement, exercise, digestion and other activity add to daily energy use. Tervilo's BMR calculator presents equation-based estimates and makes that distinction explicit.
What BMR means
BMR is intended to represent baseline energy expenditure. Because it is an estimated value rather than a direct measurement for most people, the number should be treated as a useful reference point rather than an exact personal constant.
Mifflin–St Jeor equation
One common adult estimation method is the Mifflin–St Jeor equation. For men, the equation is:
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5For women, the corresponding constant is minus 161 rather than plus 5.
Revised Harris–Benedict
Another established estimation approach is the revised Harris–Benedict equation. The important point is that equations can produce different estimates because they use different coefficients. A calculator guide should state which approach is being used rather than implying that every BMR calculation has one universal answer.
How to use Tervilo's BMR Calculator
- Open the Tervilo BMR Calculator.
- Enter age, sex, height and weight as requested.
- Review the estimated BMR.
- Read the notes about activity and daily energy needs.
Worked example
Using the Mifflin–St Jeor equation, a hypothetical 30-year-old man weighing 70 kg and standing 175 cm would have an estimated BMR of about 1,649 kcal/day. That number describes the equation's estimate of resting energy use; it is not his full daily calorie requirement.
BMR vs TDEE
BMR is the baseline estimate. TDEE is a broader estimate that accounts for activity and other daily energy expenditure. A calorie calculator can use BMR as one input into an estimate of total daily needs.
Why two BMR calculators can disagree
Different formulas, rounding conventions and input assumptions can create different results. A small numerical difference is not evidence that one calculator is necessarily wrong. The formula and inputs matter.
Limitations of equation-based BMR
Age, body composition, genetics, illness, medications and other factors can affect actual energy expenditure. Equation-based estimates cannot observe all of them. They are therefore best used for planning and comparison rather than false precision.
When BMR is not enough
BMR does not tell you how many calories to eat, how much exercise you need or whether a specific diet is medically appropriate. For individualized health or nutrition decisions, professional guidance is more appropriate than relying on a single estimated number.
Why BMR equations are estimates
Resting energy expenditure is not identical from person to person with the same age, sex, height and weight. Equation-based calculators use population data and mathematical coefficients to estimate a value that is useful for planning but not guaranteed to match an individual's measured metabolism.
What BMR does not include
BMR is not a complete daily energy budget. Walking, exercise, occupational activity, digestion and other energy expenditure occur in addition to resting needs. That is why a BMR result should not be interpreted as the number of calories to eat or the number of calories you will burn in a normal day.
Example of turning BMR into a daily estimate
If a hypothetical BMR estimate is 1,650 kcal/day and a chosen activity factor is 1.4, the resulting daily estimate is 2,310 kcal/day. The arithmetic is straightforward; the uncertainty comes from the assumptions behind the BMR equation and activity level.
How to compare BMR results
When comparing two calculations, keep the input values and equation consistent. Changing the formula, units or activity assumptions can make two otherwise correct results look inconsistent.
Quick checklist
- □ I entered the correct units.
- □ I know which equation the calculator uses.
- □ I understand BMR is not total daily energy expenditure.
- □ I treated the result as an estimate.
- □ I did not use BMR alone to make medical decisions.
Quick answer
BMR estimates resting energy use from inputs such as age, sex, height and weight. Common equations include Mifflin–St Jeor and revised Harris–Benedict. BMR is not the same as TDEE, and the result should be treated as an estimate rather than an exact measurement.