Which BMR formula is most accurate?

For most healthy adults, the Mifflin–St Jeor equation is widely recommended by researchers for its accuracy. If you know your body fat percentage, Katch–McArdle can be very precise.

What’s the difference between BMR and TDEE?

BMR is the calories your body needs at rest. TDEE is your daily calories factoring in activity level (BMR multiplied by an activity factor).

Should I use metric or US units?

Use whichever you’re comfortable with. The calculator converts internally to keep results consistent.

Do age and sex matter for BMR?

Yes. BMR generally decreases with age, and males often have higher BMR than females due to body composition differences.

What if my weight changes?

Recalculate. BMR and TDEE change with weight, especially with significant gains or losses.

Is this medical advice?

No. This tool provides educational estimates. Consult a qualified healthcare professional for personalized guidance.

BMR (Basal Metabolic Rate) Calculator

Estimate basal metabolic rate using standard equations and inputs.

Calculator

Metric US / Imperial

Sex at birth *

Male Female

Age *

Enter age in whole years (10–120).

Height *

Weight *

Formula *

Mifflin–St Jeor Harris–Benedict Katch–McArdle

Activity level

Educational purposes only. Not medical advice.

Results

BMR (kcal/day) —

TDEE (kcal/day) —

Mild weight loss target (−15%) —

Mild weight gain target (+10%) —

Estimates are rounded. Individual needs vary by genetics, hormones, and body composition.

Data Source and Methodology

This calculator implements three peer‑reviewed, widely cited equations:

Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241–247. DOI: 10.1093/ajcn/51.2.241. Source
Harris JA, Benedict FG. A Biometric Study of Basal Metabolism in Man. 1919; plus revisions (Roza & Shizgal, 1984). Revised coefficients
Katch VL, McArdle WD. Nutrition, Weight Control, and Exercise. Houghton Mifflin; 1977. Fat‑free mass based REE estimation.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formulas Explained

Mifflin–St Jeor:

Male: $ \mathrm{BMR} = 10\,w + 6.25\,h - 5\,a + 5 $

Female: $ \mathrm{BMR} = 10\,w + 6.25\,h - 5\,a - 161 $

where w = weight (kg), h = height (cm), a = age (years)

Revised Harris–Benedict (Roza & Shizgal 1984):

Male: $ \mathrm{BMR} = 13.397\,w + 4.799\,h - 5.677\,a + 88.362 $

Female: $ \mathrm{BMR} = 9.247\,w + 3.098\,h - 4.330\,a + 447.593 $

Katch–McArdle:

$ \mathrm{BMR} = 370 + 21.6 \times \mathrm{LBM} $, with $ \mathrm{LBM} = w \times (1 - \mathrm{bf}) $

bf = body fat fraction (e.g., 20% → 0.20)

Activity factor (TDEE): $ \mathrm{TDEE} = \mathrm{BMR} \times \mathrm{AF} $

Glossary of Variables

Age (years): Age in whole years.
Height (cm or ft/in): Body height. Converted to centimeters for computation.
Weight (kg or lb): Body mass. Converted to kilograms for computation.
Body fat %: Percentage of body weight from fat. Used for Katch–McArdle only.
BMR (kcal/day): Basal Metabolic Rate: calories needed at complete rest.
TDEE (kcal/day): Total Daily Energy Expenditure: BMR multiplied by an activity factor.

How It Works: A Step‑by‑Step Example

Scenario: Male, 30 years, 180 cm, 75 kg, Moderately active (AF=1.55), formula: Mifflin–St Jeor.

Compute BMR: $ 10 \times 75 + 6.25 \times 180 - 5 \times 30 + 5 = 750 + 1125 - 150 + 5 = 1730\ \mathrm{kcal/day} $.
Estimate TDEE: $ 1730 \times 1.55 \approx 2682\ \mathrm{kcal/day} $.
Mild weight loss target (−15%): $ 2682 \times 0.85 \approx 2280\ \mathrm{kcal/day} $.
Mild weight gain target (+10%): $ 2682 \times 1.10 \approx 2950\ \mathrm{kcal/day} $.

Frequently Asked Questions (FAQ)

Is BMR the same as RMR?

No. BMR is measured under stricter lab conditions than Resting Metabolic Rate (RMR). Many tools use the terms interchangeably, but BMR estimates are generally slightly lower than RMR.

Which formula should I choose?

Mifflin–St Jeor is a strong default for most adults. If you reliably know your body fat percentage, Katch–McArdle can be very precise. Harris–Benedict is a classic alternative.

How accurate are these estimates?

They’re population-based models. Individual metabolism can deviate due to genetics, hormonal status, medications, and lean mass. Treat results as starting points.

What activity factor should I use?

Pick the one that best reflects your weekly training and occupation. If unsure, start lower and adjust based on weight trends.

Do I need to change calories every day?

Short-term fluctuations are normal. Reassess every 2–4 weeks and adjust calories if average weight changes differ from your target trend.

Can this calculator help with macros?

It focuses on energy needs. For macronutrient planning, use a dedicated macro calculator after establishing TDEE.

Is there a medical restriction?

If you have medical conditions, are pregnant, or under 18, consult a qualified professional. This tool is not medical advice.

Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

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Formula (extracted LaTeX)

\[= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); // Elements const unitsMetric = $('#unitsMetric'); const unitsUS = $('#unitsUS'); const sexMale = $('#sexMale'); const sexFemale = $('#sexFemale'); const age = $('#age'); const heightCm = $('#heightCm'); const heightFt = $('#heightFt'); const heightIn = $('#heightIn'); const weightKg = $('#weightKg'); const weightLb = $('#weightLb'); const heightMetricGroup = $('#heightMetricGroup'); const heightUSGroup = $('#heightUSGroup'); const weightMetricGroup = $('#weightMetricGroup'); const weightUSGroup = $('#weightUSGroup'); const formulaRadios =\]

= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); // Elements const unitsMetric = $('#unitsMetric'); const unitsUS = $('#unitsUS'); const sexMale = $('#sexMale'); const sexFemale = $('#sexFemale'); const age = $('#age'); const heightCm = $('#heightCm'); const heightFt = $('#heightFt'); const heightIn = $('#heightIn'); const weightKg = $('#weightKg'); const weightLb = $('#weightLb'); const heightMetricGroup = $('#heightMetricGroup'); const heightUSGroup = $('#heightUSGroup'); const weightMetricGroup = $('#weightMetricGroup'); const weightUSGroup = $('#weightUSGroup'); const formulaRadios =

Formula (extracted text)

Mifflin–St Jeor: Male: \( \mathrm{BMR} = 10\,w + 6.25\,h - 5\,a + 5 \) Female: \( \mathrm{BMR} = 10\,w + 6.25\,h - 5\,a - 161 \) where w = weight (kg), h = height (cm), a = age (years) Revised Harris–Benedict (Roza & Shizgal 1984): Male: \( \mathrm{BMR} = 13.397\,w + 4.799\,h - 5.677\,a + 88.362 \) Female: \( \mathrm{BMR} = 9.247\,w + 3.098\,h - 4.330\,a + 447.593 \) Katch–McArdle: \( \mathrm{BMR} = 370 + 21.6 \times \mathrm{LBM} \), with \( \mathrm{LBM} = w \times (1 - \mathrm{bf}) \) bf = body fat fraction (e.g., 20% → 0.20) Activity factor (TDEE): \( \mathrm{TDEE} = \mathrm{BMR} \times \mathrm{AF} \)

Variables and units

No variables provided in audit spec.

Sources (authoritative):

Revised coefficients — pubmed.ncbi.nlm.nih.gov · Accessed 2026-01-19
https://pubmed.ncbi.nlm.nih.gov/6741853/
Source — academic.oup.com · Accessed 2026-01-19
https://academic.oup.com/ajcn/article-abstract/51/2/241/4695071

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
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