Science & Methodology

Health Metrics Science

How your numbers are calculated — formulas, accuracy, and certified references

Health metrics displayed on this platform are calculated using globally validated clinical formulas (Mifflin-St Jeor for BMR, Deurenberg for body fat, WHO BMI classifications). These figures are evidence-based estimates derived from your provided measurements and are intended to support, not replace, professional health advice. Actual values can vary by ±5–15% depending on individual physiology. All metric calculations are performed following ICMR-NIN Dietary Guidelines 2024 and WHO health standards. For clinical diagnosis or treatment decisions, please consult a qualified healthcare professional.

What does ~ mean?

The ~ symbol indicates a calculated estimate. Values are computed from scientifically validated formulas and are updated automatically as your measurements change.

Standards We Follow

🌍 WHO — Obesity & Overweight, Healthy Diet, Physical Activity Guidelines
🇮🇳 ICMR-NIN — Dietary Guidelines for Indians 2024, Recommended Dietary Allowances
🇮🇳 National Health Portal — Government of India BMI classifications
🇮🇳 MoHFW — Ministry of Health & Family Welfare nutrition standards

BMI — Body Mass Index

BMI = Weight (kg) ÷ Height² (m)

Formula Source

Adolphe Quetelet (1832) · Adopted by WHO as a population screening tool

What It Means

BMI gives a quick numerical snapshot of whether your weight is proportionate to your height. It is widely used by health organisations globally as an initial screening tool.

How to Use It

Use BMI as one of several indicators — not in isolation. A person with high muscle mass may show a higher BMI while having a healthy body composition. Pair BMI with body fat percentage and waist measurements for a more complete picture.

Accuracy & Limitations

BMI is a population-level screening indicator. At an individual level, it does not distinguish between muscle mass, bone density, or fat distribution.

BMI does not directly measure body fat. Athletes, older adults, and individuals with higher muscle mass may have different interpretations than the general population.

Certified References

WHO — Obesity & Overweight

World Health Organization

NHLBI — Calculate Your BMI

National Heart, Lung, and Blood Institute (NIH, USA)

ICMR-NIN Dietary Guidelines for Indians 2024

ICMR — National Institute of Nutrition

BMR — Basal Metabolic Rate

Mifflin-St Jeor: Men = (10 × kg) + (6.25 × cm) − (5 × age) + 5 | Women = same − 161

Formula Source

Mifflin MD, St Jeor ST et al. (1990) — validated in clinical nutrition research

What It Means

BMR is the number of calories your body needs to maintain basic life functions — breathing, circulation, and cell repair — even at complete rest. It is your energy baseline.

How to Use It

BMR is the foundation for calculating your daily calorie needs. Your coach uses it alongside your activity level to set a personalised calorie target.

What ~ Means for This Metric

The ~ symbol indicates this is a scientifically calculated estimate. Individual BMR can vary by roughly ±10% depending on body composition and metabolic factors.

Accuracy & Limitations

The Mifflin-St Jeor formula has an average variance of ±10% for individuals. Actual BMR can differ based on body composition, hormonal factors, and metabolic health.

BMR is calculated from population-level equations. Actual values vary by individual. It is a starting point for personalised nutrition planning, refined over time through tracking.

Certified References

WHO — Healthy Diet

World Health Organization

ICMR-NIN Dietary Guidelines for Indians 2024

ICMR — National Institute of Nutrition

MoHFW (FSSAI) — Eat Right India

Ministry of Health & Family Welfare, Govt. of India

TDEE — Total Daily Energy Expenditure

TDEE = BMR × Activity Multiplier (1.2 – 1.9 depending on lifestyle)

Formula Source

Harris-Benedict activity scale, refined by Ainsworth et al. Compendium of Physical Activities

What It Means

TDEE is the total calories your body burns in a day — at rest plus all your movement and exercise. Eating below TDEE leads to fat loss; eating above builds mass.

How to Use It

Eating 300–500 kcal below TDEE supports safe, sustainable fat loss (~0.3–0.5 kg/week). Eating 200–400 kcal above supports gradual muscle gain. Your coach sets this target based on your goal.

What ~ Means for This Metric

The ~ symbol means this is a calculated estimate of your daily energy needs. Real-world values depend on the accuracy of your reported activity level.

Accuracy & Limitations

TDEE estimates carry the same ±10% individual variance as BMR, further compounded by how accurately activity level is self-reported.

TDEE is based on your self-reported activity level, which is often slightly overestimated. Real-world tracking over 2–3 weeks of consistent eating is the most reliable way to calibrate it.

Certified References

WHO — Healthy Diet

World Health Organization

WHO — Physical Activity

World Health Organization

ICMR-NIN Dietary Guidelines for Indians 2024

ICMR — National Institute of Nutrition

Body Fat % — Estimated Body Fat Percentage

Deurenberg: Men = (1.20 × BMI) + (0.23 × age) − 16.2 | Women = same − 10.8

Formula Source

Deurenberg P, Weststrate JA, Seidell JC (1991) — BMI-based body fat estimation

What It Means

Body fat percentage represents the proportion of your total body weight that is fat tissue. It is a more nuanced indicator of body composition than BMI alone.

How to Use It

Use body fat % as a directional indicator alongside your weight and BMI. A downward trend over months, combined with maintained or improved strength, indicates healthy body recomposition.

What ~ Means for This Metric

The ~ symbol indicates this is a population-level estimation, not a direct measurement. Clinical measurements (DEXA scan, hydrostatic weighing) provide higher individual accuracy.

Accuracy & Limitations

This BMI-based method has a standard error of approximately ±3–5 percentage points. It is a population-level estimate and may overestimate body fat in individuals with high muscle mass.

This estimation is derived from BMI and age using a validated clinical formula. Direct body fat measurement requires specialised equipment (DEXA, BIA, skinfold calipers) available in clinical settings.

Certified References

WHO — Obesity & Overweight

World Health Organization

NHLBI — Calculate Your BMI

National Heart, Lung, and Blood Institute (NIH, USA)

ICMR-NIN Dietary Guidelines for Indians 2024

ICMR — National Institute of Nutrition

Protein Target — Daily Protein Requirement

Fat Loss: 0.8–1.2 g/kg · Recomposition: 1.2–1.6 g/kg · Muscle Gain: 1.5–2.0 g/kg

Formula Source

ICMR-NIN Dietary Guidelines 2024 · WHO Healthy Diet guidelines · Sports nutrition research consensus

What It Means

Protein is essential for repairing and building muscle tissue, producing hormones and enzymes, and supporting immune function. The "At Least" value is the science-backed daily floor for your goal.

How to Use It

Aim to consistently hit the "At Least" figure each day. Distribute your protein across 3–5 meals (20–40 g per meal) for optimal absorption. Whole food sources — dairy, legumes, poultry, fish, eggs — are preferred.

Accuracy & Limitations

Protein requirements are individualised. The ranges provided are evidence-based consensus values for active adults. Needs may differ based on age, kidney health, and training intensity.

These targets are calculated from your body weight and training goal. Individuals with kidney disease, specific health conditions, or very different activity levels should consult a registered dietitian.

Certified References

ICMR-NIN — Recommended Dietary Allowances for Indians

ICMR — National Institute of Nutrition

ICMR-NIN Dietary Guidelines for Indians 2024

ICMR — National Institute of Nutrition

WHO — Healthy Diet

World Health Organization

MoHFW (FSSAI) — Eat Right India

Ministry of Health & Family Welfare, Govt. of India

Legal Disclaimer

Health metrics provided by BrixFit are calculated using internationally validated clinical formulas and are intended for general wellness guidance only. They do not constitute medical advice, diagnosis, or treatment. Users should consult a qualified healthcare professional for clinical assessment and treatment decisions.

All metric calculations comply with ICMR-NIN Dietary Guidelines 2024 and WHO health standards. Results are estimates and can vary by individual physiology, measurement accuracy, and health conditions.