Macro Calculator — Free 2026

Understanding Macronutrients and Why They Matter

Macronutrients — protein, carbohydrates, and fat — are the three essential nutrients your body requires in large amounts to function properly. Unlike micronutrients (vitamins and minerals), which are needed in tiny quantities, macronutrients provide the energy (measured in calories) that powers everything from basic cellular processes to intense physical activity. Each macronutrient plays a unique and irreplaceable role in your body, and the ratio in which you consume them can significantly impact your health, body composition, and performance.

The concept of tracking macros, sometimes called "flexible dieting" or "If It Fits Your Macros" (IIFYM), has become popular because it offers a more nuanced approach to nutrition than simply counting calories. Two diets with the same calorie count can produce very different results depending on whether those calories come primarily from protein, carbohydrates, or fat. A 2,000-calorie diet composed of 40% protein and 30% carbs will support muscle growth far more effectively than a 2,000-calorie diet with only 10% protein, even though the total energy is identical.

The Mifflin-St Jeor Equation Explained

This calculator uses the Mifflin-St Jeor equation, which research has shown to be one of the most accurate methods for estimating Basal Metabolic Rate (BMR) in healthy adults. Published in 1990 by Mifflin, St Jeor, and colleagues, the equation was validated against indirect calorimetry and found to predict BMR within 10% for the majority of individuals — a better track record than older formulas like the Harris-Benedict equation (1919) or the Katch-McArdle formula, which requires a body fat percentage measurement.

The formula works as follows. For men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5. For women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161. Your BMR is then multiplied by an activity factor — ranging from 1.2 for sedentary individuals to 1.9 for those with extremely demanding physical activity — to estimate your Total Daily Energy Expenditure (TDEE). This TDEE represents the total number of calories you burn in a typical day, including exercise and non-exercise activity.

From there, a goal adjustment is applied. For weight loss, the calculator reduces your TDEE by 20%, creating a moderate calorie deficit that supports fat loss while preserving muscle mass. For weight gain, it adds 15% to your TDEE, providing a surplus to fuel muscle growth without excessive fat accumulation. Maintaining weight uses your TDEE as-is.

Breaking Down the Three Macronutrients

Protein is the building block of muscle, skin, enzymes, and hormones. It provides 4 calories per gram. Beyond muscle repair, adequate protein intake has been linked to improved satiety (feeling full after meals), better blood sugar control, and a higher thermic effect of food — meaning your body burns more calories digesting protein than it does digesting carbs or fat. The recommended dietary allowance (RDA) for protein is 0.8g per kilogram of body weight, but most sports nutrition research suggests 1.6-2.2g per kilogram for people engaged in regular resistance training.

Carbohydrates are your body's preferred energy source, providing 4 calories per gram. They are stored as glycogen in your muscles and liver, fuelling everything from high-intensity exercise to brain function. Complex carbohydrates — found in whole grains, vegetables, and legumes — provide sustained energy and fibre, while simple carbohydrates (sugar, white bread) cause rapid blood sugar spikes. The amount of carbohydrate you need depends heavily on your activity level: endurance athletes may need 7-10g per kilogram of body weight, while sedentary individuals do well on 3-5g per kilogram.

Fat is essential for hormone production (including testosterone and oestrogen), absorption of fat-soluble vitamins (A, D, E, K), brain health, and cell membrane integrity. Fat provides 9 calories per gram — more than twice as calorie-dense as protein or carbs. This is why low-fat diets fell out of favour: cutting fat too aggressively can impair hormone function and leave you chronically hungry. The American Heart Association recommends that 20-35% of total calories come from fat, with an emphasis on unsaturated fats from sources like olive oil, nuts, avocado, and fatty fish.

Choosing the Right Diet Type

The four diet types available in this calculator represent common macro splits used in nutrition planning:

• Balanced (30/40/30): A well-rounded split suitable for most people. Moderate protein, ample carbohydrates for energy, and sufficient fat for hormone health. This is a safe starting point if you are unsure which split to choose.
• High Protein (40/30/30): Ideal for people focused on building or preserving muscle, especially during a calorie deficit. Higher protein intake maximises muscle protein synthesis and satiety.
• Low Carb (35/25/40): Reduces carbohydrate intake while increasing fat. Popular among people with insulin resistance or those who find they feel better with fewer carbs. Still provides enough carbs to fuel moderate exercise.
• Keto (30/5/65): A very low-carbohydrate, high-fat approach that pushes the body into ketosis — a metabolic state where fat becomes the primary fuel source. Effective for some people's weight loss but requires careful planning to avoid nutrient deficiencies.

To track your body composition progress alongside your macro targets, consider using our BMI calculator as a baseline measurement. If you want to estimate your daily calorie burn from a different angle, our calorie calculator offers an alternative approach.

Fibre: The Forgotten Nutrient

While not technically a macronutrient in the energy-providing sense, dietary fibre is a critical component of a healthy diet. The general recommendation is approximately 14 grams of fibre per 1,000 calories consumed, which this calculator estimates for you. Adequate fibre intake supports digestive health, helps regulate blood sugar levels, promotes satiety, and has been associated with reduced risk of cardiovascular disease, type 2 diabetes, and colorectal cancer. Most adults in Western countries consume only about half the recommended amount, making it one of the most common nutritional shortfalls.

Adjusting Your Macros Over Time

No calculator can perfectly predict your individual metabolic response. The numbers provided here are an evidence-based starting point, not a permanent prescription. Weigh yourself under consistent conditions (same time of day, same clothing) and track trends over 2-4 weeks. If you are losing weight too quickly (more than 1% of body weight per week), increase your calories slightly. If progress has stalled, you may need a small reduction or a reassessment of your activity level. Body composition changes are best measured over months, not days, so patience and consistency are far more important than precision in hitting exact macro targets.