How accurate is this calorie and macro calculator?

This calculator uses the Mifflin-St Jeor equation, which predicts BMR within 10% for 82% of individuals according to the American Dietetic Association. It is the most validated equation for estimating resting metabolic rate.

What are macronutrients and why do they matter?

Macronutrients are the three main nutrients your body needs in large amounts: protein (4 cal/g), carbohydrates (4 cal/g), and fat (9 cal/g). Each serves distinct functions — protein builds and repairs tissue, carbs fuel activity, and fats support hormones and cell function.

Should I adjust my macros on rest days?

Some people benefit from reducing carbs 10-20% on rest days while keeping protein consistent. For most recreational exercisers, keeping macros consistent daily is simpler and equally effective.

How often should I recalculate my calorie and macro needs?

Recalculate after any 5+ pound weight change, a significant change in activity level, or every 4-6 weeks during active dieting phases.

What is the best macro split for weight loss?

Higher protein (25-35% of calories, or 1.6-2.2 g/kg body weight) helps preserve muscle during a deficit. A 30% protein / 40% carbs / 30% fat split works well for most people losing weight.

How much protein do I need per day?

The ISSN recommends 1.4-2.0 g/kg for active individuals. During a calorie deficit, aim for 1.6-2.2 g/kg to preserve lean muscle mass.

What should you eat?

Science-based calorie and macro targets for your goal

Sex

Age

Weight (kg)

Weight (lbs)

Height (cm)

Activity Level

Goal

Diet Preference

calories per day

Protein

Carbs

Fat

Your nutrition breakdown

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Medical Disclaimer: This tool provides general educational estimates. Always consult your prescribing physician or healthcare provider before making medication changes or interpreting results from population-based models.

Frequently Asked Questions

This calculator uses the Mifflin-St Jeor equation, which predicts BMR within 10% for 82% of individuals according to the American Dietetic Association. It is the most validated equation for estimating resting metabolic rate.
Macronutrients are the three main nutrients your body needs in large amounts: protein (4 cal/g), carbohydrates (4 cal/g), and fat (9 cal/g). Each serves distinct functions -- protein builds and repairs tissue, carbs fuel activity, and fats support hormones and cell function.
Some people benefit from reducing carbs 10-20% on rest days while keeping protein consistent. For most recreational exercisers, keeping macros consistent daily is simpler and equally effective.
Recalculate after any 5+ pound weight change, a significant change in activity level, or every 4-6 weeks during active dieting phases.
Higher protein (25-35% of calories, or 1.6-2.2 g/kg body weight) helps preserve muscle during a deficit. A 30% protein / 40% carbs / 30% fat split works well for most people losing weight.
The ISSN recommends 1.4-2.0 g/kg for active individuals. During a calorie deficit, aim for 1.6-2.2 g/kg to preserve lean muscle mass.

Sources

Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. Link
Jäger R, et al. International Society of Sports Nutrition Position Stand: Protein and Exercise. J Int Soc Sports Nutr. 2017;14:20. Link
Dietary Guidelines for Americans 2020-2025. U.S. Department of Agriculture. Link
Thomas DT, et al. Position of the Academy of Nutrition and Dietetics: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501-528. Link

Methodology

Uses the Mifflin-St Jeor equation (1990). Males: BMR = (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5. Females: same formula minus 161 instead of plus 5. TDEE = BMR × activity factor (1.2-1.9). Goal adjustments range from -500 to +500 kcal/day. Macronutrient distribution follows ISSN and Academy of Nutrition and Dietetics guidelines.

The Mifflin-St Jeor equation estimates BMR: Males = (10×weight kg) + (6.25×height cm) - (5×age) + 5. TDEE = BMR × activity factor (1.2-1.9). Macro splits: Balanced 30/40/30 P/C/F, Low-Carb 30/25/45, High-Carb 25/55/20, Keto 20/5/75. Protein and carbs provide 4 cal/g, fat provides 9 cal/g.

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