By Zencalcy Editorial TeamLast reviewed About us
The Harris-Benedict equation is one of the oldest published formulas for estimating basal metabolic rate. The original 1919 version was later revised to better fit modern populations, and both variants are still used in nutrition and clinical settings. This calculator lets you choose either equation and shows the full arithmetic for your inputs.
Compare the original and revised Harris-Benedict BMR equations.
| Equation version |
Original men: 66.5 + 13.75w + 5.003h - 6.775a Original women: 655.1 + 9.563w + 1.850h - 4.676a Revised men: 88.362 + 13.397w + 4.799h - 5.677a Revised women: 447.593 + 9.247w + 3.098h - 4.330a
w is weight in kilograms, h is height in centimetres and a is age in years. The revised equation generally returns a slightly lower value than the original for the same person. As with every predictive equation, the result is an average estimate rather than a measurement.
| Symbol | Meaning |
|---|---|
| w | Body weight in kilograms. |
| h | Standing height in centimetres. |
| a | Age in years. |
| BMR | Basal metabolic rate in kilocalories per day. |
Original: 66.5 + 13.75 x 80 + 5.003 x 180 - 6.775 x 30 = 1863.79, which rounds to 1863.8 kcal per day. Revised: 88.362 + 13.397 x 80 + 4.799 x 180 - 5.677 x 30 = 1853.632, which rounds to 1853.6 kcal per day.
The Harris-Benedict equation was derived from indirect calorimetry data collected in the early twentieth century. As living standards, body composition and measurement methods changed, researchers refitted the equation to newer data, producing the revised version. The structure stayed the same: a constant plus weighted terms for weight, height and age. What changed were the coefficients and the sex-specific constants. For a typical adult the revised equation returns a slightly lower BMR, often by 10 to 30 calories. That difference is small compared with the error of any prediction, which is why the choice between versions matters less than tracking your actual weight response. Use the equation that matches the source you are following, record which one you used, and adjust from real-world feedback.
Continue with the BMR Calculator (Mifflin-St Jeor), Katch-McArdle Calculator, or the RMR Calculator (Resting Metabolic Rate) — or browse more dietary tools and all health calculators.
Also see the Calorie Calculator, TDEE Calculator and the Macro Calculator.
The revised equation is usually the better default because it was fitted to a later population and tends to predict slightly lower values. The original remains useful for comparison and appears in older clinical formulas.
Energy and nutrient estimates are population guidance, not personal prescriptions. Actual needs vary with body composition, medical conditions, medication, pregnancy and activity. Values are rounded and should be discussed with a registered dietitian or clinician when used to plan treatment.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026