BMR (Harris–Benedict) + TDEE Calculator
Estimate basal metabolic rate and daily calorie needs using the Harris–Benedict equation and an activity multiplier.
A Harris Benedict Calculator estimates basal metabolic rate from age, sex, height and weight. The revised equations predict energy use under standardized resting assumptions; they do not directly measure metabolism or automatically equal maintenance calories.
Enter the Harris–Benedict Variables
The calculator uses the original Harris–Benedict equations:
Male: BMR = 66.5 + (13.75 × weight in kg) + (5.003 × height in cm) − (6.755 × age)
Female: BMR = 655.1 + (9.563 × weight in kg) + (1.850 × height in cm) − (4.676 × age)
Daily calorie needs are then estimated with:
TDEE = BMR × activity factor
Revised Harris-Benedict Calculator Equations
For a 30-year-old male weighing 80 kg and measuring 180 cm:
BMR = 66.5 + (13.75 × 80) + (5.003 × 180) − (6.755 × 30)
BMR ≈ 1,864 calories/day
Using a moderate activity factor of 1.55:
TDEE ≈ 1,864 × 1.55 = 2,890 calories/day
This gives an estimated maintenance intake of approximately 2,890 calories per day.
Worked BMR Estimate
The Harris–Benedict equation predicts energy needs from age, sex, height, and weight. It does not directly measure metabolism or body composition, so actual calorie needs can differ.
Use the result as a starting estimate and adjust according to real body-weight trends, activity, and health circumstances.
Basal Rate Versus Daily Energy Needs
Metric Conversion and Rounding
The Harris-Benedict Calculator (Basal Metabolic Rate) is designed to estimate basal energy expenditure using a Harris–Benedict equation. It is an educational planning tool: the result becomes useful only when the inputs are accurate, the units match, and the output is interpreted in the right personal or clinical context.
- Read each field label and enter age, sex, height, and weight in the requested units.
- Confirm dates, units, laboratory analytes, or measurement methods before calculating.
- Select Calculate and review the main result together with any range, category, or supporting values.
- Keep extra precision during the calculation, then round only to a level supported by the original measurements.
- Compare the result with the limitations and safety notes below before acting on it.
Prediction Error and Individual Variation
The output represents an estimate of energy used at rest before an activity factor is applied. It should be treated as an estimate or standardized calculation, not as a complete assessment of health. A number can organize information and support a conversation, but it cannot account for symptoms, examination findings, laboratory quality, personal history, or every factor a qualified professional would consider.
When a category or range is displayed, first check which guideline, population, age group, sex, formula, or reference dataset the calculator uses. Different reputable methods may produce different results without either calculation being mathematically wrong.
When the Equation Is Not Appropriate
Good output begins with good input. Use current measurements, enter decimals carefully, and do not mix metric and U.S. customary units unless the calculator converts them explicitly. For body measurements, use the same technique each time. For dates, confirm the calendar entry. For laboratory values or medication quantities, copy the value, analyte, unit, concentration, and timing directly from the verified report or label.
If a result looks implausible, do not simply accept it. Recheck transposed digits, misplaced decimal points, unit selections, age, sex, dates, and whether the value belongs to the correct person. Recalculate from the original source rather than from a rounded previous result.
Use BMR as a Starting Estimate
The calculator applies the equation, reference method, or conversion described in the existing formula section of this page. Some tools use a direct mathematical relationship, while others apply population averages, reference curves, or activity factors. A precise-looking answer can still carry substantial uncertainty when the underlying method is predictive rather than directly measured.
For a useful manual check, follow the displayed substitution step by step and confirm that the direction of the result makes sense. Changing one input at a time can also show which variable most strongly influences the estimate. Do not reverse a clinical formula or reuse a conversion factor for a different substance unless an authoritative reference specifically permits it.
Accuracy, Limitations, and Individual Variation
The equation predicts an average from population data and does not directly measure metabolism. Body composition, illness, pregnancy, and individual variation can cause differences.
Repeated measurements under similar conditions are often more informative than a single isolated value. Record the date, method, units, and relevant circumstances so that later comparisons are meaningful. A change may reflect real physiology, measurement technique, hydration, timing, device variation, or ordinary day-to-day fluctuation.
Using the Result Responsibly
This page provides general educational information and does not diagnose a condition, prescribe treatment, or replace professional care. Do not start, stop, or change medication, supplements, fluid restrictions, nutrition therapy, anticoagulation, or pregnancy care because of an online result. Seek prompt medical help for severe or rapidly worsening symptoms, and use local emergency services when a situation may be life-threatening.
For additional context, consult the CDC healthy-weight guidance. A clinician, pharmacist, registered dietitian, or other qualified professional can explain how the estimate applies to an individual situation and whether confirmatory testing is appropriate.
Related Health Calculators
Explore the Maintenance Calorie Calculator and BMR — Basal Metabolic Rate (Mifflin–St Jeor) for related planning or measurement support. Use each calculator according to its own inputs and limitations rather than transferring a result or factor between tools.
Before You Compare Results Over Time
Use the same calculator, formula, units, device, and measurement technique for every comparison. Where practical, collect measurements at a similar time of day and under similar conditions. A small change may be caused by rounding or normal variation rather than a meaningful health change.
Look for a consistent pattern and keep the underlying values, not only the calculated output. If the direction of change is unexpected, first verify the original inputs. For clinical measurements, laboratory values, pregnancy dates, child growth, or medication-related calculations, ask the relevant professional how often the value should be reassessed and what size of change is important.
The original and revised equations differ
Harris and Benedict published early equations in 1919; later researchers re-evaluated the relationship using newer data. Check which version a calculator implements before comparing outputs, and avoid mixing coefficients from different versions.
Predicted BMR is not a calorie prescription
Activity, thermic effect of food and adaptation affect total needs. The revised equation was evaluated by Roza and Shizgal; see the study record in PubMed. Clinical nutrition decisions require qualified assessment.
Frequently Asked Questions
What does the Harris-Benedict Calculator (Basal Metabolic Rate) estimate?
It is designed to estimate basal energy expenditure using a Harris–Benedict equation. The answer is an estimate of energy used at rest before an activity factor is applied. Read the method and limitations before interpreting the number.
Which inputs affect the result most?
The required inputs are age, sex, height, and weight in the requested units. The most influential field depends on the equation, so each value and unit should be checked rather than assuming one input is unimportant.
How accurate is this calculator?
The arithmetic is repeatable, but real-world accuracy depends on measurement quality and how well the selected formula or reference represents the person and situation. Predictive tools should be understood as estimates.
Can this result diagnose a health condition?
No. A calculator cannot evaluate symptoms, medical history, examination findings, test quality, or competing explanations. Use the result for education or discussion with an appropriate professional.
Why is my result different from another calculator?
The other tool may use a different equation, reference population, rounding rule, activity factor, laboratory convention, or unit conversion. Compare methods and inputs before comparing the final numbers.
When should I speak with a healthcare professional?
Ask for professional guidance when a result is unexpected, repeatedly outside a stated reference, linked to symptoms, used for medication or clinical decisions, or affected by pregnancy, childhood, chronic disease, or major body changes.
