What is the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation is a validated formula for estimating Basal Metabolic Rate (BMR). Published in 1990, it is considered more accurate than the older Harris-Benedict equation. It uses weight, height, age, and sex as inputs.

What is the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain basic physiological functions. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to account for movement, exercise, and daily activities.

How are macros calculated?

Macros are calculated as a percentage of your target daily calories. This calculator uses a standard distribution: 30% protein (4 kcal/g), 40% carbohydrates (4 kcal/g), and 30% fat (9 kcal/g). Fiber is estimated at 14g per 1,000 kcal consumed.

How much protein do I need per day?

Protein needs vary by goal and body weight. General guidelines recommend 0.8g/kg for sedentary adults (WHO/RDA), 1.2–1.6g/kg for active adults, and up to 1.6–2.2g/kg for those building muscle (ISSN position stand). This calculator uses 30% of target calories from protein.

How much water should I drink per day?

This calculator uses the commonly cited estimate of 33ml per kg of body weight per day. The National Academies of Medicine recommends approximately 3.7L/day for men and 2.7L/day for women from all sources (food and beverages). Individual needs vary based on climate, activity, and health status.

Is this calculator accurate for everyone?

The Mifflin-St Jeor equation provides estimates with approximately ±10% accuracy for most adults aged 18–80. It may be less accurate for very muscular individuals, people with metabolic conditions, or extreme body compositions. Always consult a registered dietitian for personalized nutrition guidance.

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Macro & Calorie Calculator

Calculate your daily calorie needs, macronutrient targets, BMI, and hydration goal using the clinically validated Mifflin-St Jeor equation — the gold standard for BMR estimation since 1990.

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Your Details

Goal

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Biological Sex

MaleFemale

Used for Mifflin-St Jeor BMR formula (sex-specific constant).

Age (years)

Formula validated for ages 18–80.

Height Unit

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Height (cm)

Weight Unit

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Weight (kg)

Daily Steps (Average)

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Structured Exercise Frequency

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Activity multiplier takes the higher of steps vs. exercise to avoid double-counting.

Your Results

Your personalised daily nutrition and hydration recommendations

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Calculate My Macros

Results appear here instantly

Results are estimates based on the Mifflin-St Jeor equation (1990). Individual results vary. Consult a registered dietitian or healthcare professional before making changes to your diet or exercise regimen.

Using Your Results

How to apply your macro targets

Understanding your numbers is only the first step. Here's how to put them to use effectively.

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Use BMR as your floor

Your BMR is the minimum calories needed to sustain life at rest. Never eat below your BMR for extended periods — it triggers metabolic adaptation and muscle loss.

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TDEE is your maintenance

Eating at TDEE keeps your weight stable. A 500 kcal daily deficit from TDEE yields roughly 0.5 kg/week of fat loss — the scientifically recommended rate for preserving lean mass.

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Prioritise protein

Protein preserves muscle during a deficit, supports satiety, and has the highest thermic effect of any macro (~25–30%). Aim to hit your protein target first, then fill carbs and fat around it.

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Hydration shifts everything

Even mild dehydration (1–2% body weight) impairs cognitive performance and increases perceived hunger. Your water target is a minimum — add ~500ml per hour of exercise.

Methodology

The science behind the formulas

Every value this calculator returns is grounded in peer-reviewed research and widely accepted clinical guidelines.

Basal Metabolic Rate (BMR)

This calculator uses the Mifflin-St Jeor equation — validated in 1990 and recognized as the most accurate predictive equation for the general adult population by the Academy of Nutrition and Dietetics.

Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161

Source: Mifflin et al., Am J Clin Nutr, 1990 [1]

Total Daily Energy Expenditure (TDEE)

TDEE is calculated by multiplying BMR by an activity factor adapted from the original Harris-Benedict activity multipliers and the WHO/FAO/UNU (2004) expert consultation on human energy requirements.

Sedentary: BMR × 1.2

Lightly Active: BMR × 1.375

Moderately Active: BMR × 1.55

Very Active: BMR × 1.725

Athlete: BMR × 1.9

Source: WHO/FAO/UNU, FAO Food & Nutrition Technical Report Series 1, 2004 [7]

Macronutrient Distribution

Macro targets are calculated as a percentage of your daily calorie target, consistent with the Dietary Reference Intakes (DRI) Acceptable Macronutrient Distribution Ranges (AMDR) established by the National Academies of Sciences.

🥚 Protein: 30% of target calories ÷ 4 kcal/g

🍎 Carbohydrates: 40% of target calories ÷ 4 kcal/g

🥑 Fats: 30% of target calories ÷ 9 kcal/g

🥦 Fiber: ~14g per 1,000 kcal consumed

Source: National Academies DRI (2005) [3]; ISSN Position Stand (2017) [6]

Daily Hydration Estimate

Water target is estimated at 33ml per kg of body weight — a commonly referenced guideline aligned with the WHO and National Academies Adequate Intake (AI) for total daily water.

Formula: weight (kg) × 0.033 = litres/day

+500ml per hour of moderate exercise

Source: National Academies DRI for Water (2005) [5]; WHO guidelines

FAQs

Common questions about macros & calories

📚 Sources & References

All formulas and recommendations in this calculator are based on peer-reviewed research and clinical guidelines from recognized institutions.

[1]
Mifflin MD et al. (1990). A new predictive equation for resting energy expenditure.
American Journal of Clinical Nutrition, 51(2), 241–247.
[2]
Harris JA, Benedict FG (1918). A biometric study of human basal metabolism.
Proceedings of the National Academy of Sciences, 4(12), 370–373.
[3]
Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids.
National Academies of Sciences (2005). Institute of Medicine.
[4]
Stokes T et al. (2018). Recent perspectives regarding the role of dietary protein for the promotion of muscle hypertrophy.
Nutrients, 10(2), 180. MDPI.
[5]
Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate.
National Academies of Sciences (2005). Institute of Medicine.
[6]
Kreider RB et al. (2017). ISSN exercise & sports nutrition review update: research & recommendations.
Journal of the International Society of Sports Nutrition, 14, 33.
[7]
WHO/FAO/UNU Expert Consultation (2004). Human energy requirements.
FAO Food and Nutrition Technical Report Series 1. Rome: FAO.

Disclaimer: This calculator provides general estimates for wellness awareness purposes only. Results are not a substitute for professional medical advice, diagnosis, or treatment. Individual metabolic rates vary. Always consult a registered dietitian or licensed healthcare provider for personalised nutrition guidance.

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