BMR Calculator (Basal Metabolic Rate, Mifflin St Jeor Equation)

Written by Great Medico

Updated September 24, 2026 •2 min read

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A useful nutrition estimate should be simple enough to apply and specific enough to understand. BMR Calculator (Basal Metabolic Rate, Mifflin St Jeor Equation) focuses on one calculation at a time.

What this calculator does

Basal metabolic rate is the estimated energy required to keep basic body functions running at rest. This calculator lets you compare several established BMR equations rather than assuming one formula fits everyone equally well. Nutrition equations are planning tools: real energy and nutrient needs still vary with physiology, goals, health conditions, and the quality of the input data.

How to use it

Enter or select BMR formula, Sex, Age, Height, Weight, and Body fat. Use the units offered by the calculator and keep measurements consistent when you plan to compare results over time.

How the calculation works

Select Mifflin–St Jeor, revised Harris–Benedict, original Harris–Benedict, Katch–McArdle, or Cunningham. The first three use age, sex, height, and weight. Katch–McArdle and Cunningham use lean mass derived from the entered body-fat percentage and body weight.

Example

For the sample values prefilled in this calculator, the primary result is 1623.8 kcal/day (mifflin BMR). This example is there to show how the inputs flow through the implemented equation; replace the sample values with your own measurements before using the result.

How to interpret the result

The result is kilocalories per day at rest, before activity is added. If you change the formula, a modest difference is expected because each equation was derived from a different model and population.

Limitations and notes

BMR equations are predictions, not indirect-calorimetry measurements. Body-fat input quality matters for lean-mass formulas, and none of the equations automatically accounts for illness, pregnancy, unusually high muscle mass, or metabolic adaptation. For planning, compare the estimate with real-world trends over time instead of reacting to one day. Food-label accuracy, portion estimates, hydration, and activity can all create noise, so modest adjustments are usually more informative than chasing exact calculator precision.