What Are Macronutrients (Macros)?

When it comes to fitness and nutrition, macronutrients—often called “macros”—are the nutrients your body needs in large amounts to function and perform well. The three main macronutrients are carbohydrates, proteins, and fats. These provide the calories (energy) your body uses every day for movement, recovery, and essential functions.While some scientific definitions include things like water, sodium, or calcium, in the context of fitness and nutrition tracking, macros refer specifically to carbs, protein, and fat—the three nutrients this calculator measures.

What About Micronutrients?

Micronutrients are vitamins and minerals your body needs in much smaller amounts—usually less than 100 milligrams a day. These include vitamin A, iron, zinc, and iodine, which support everything from hormone balance to immune health.

Protein: The Building Block of Muscle

Protein is made up of amino acids—some of which your body can’t make on its own. These are called essential amino acids, and you can only get them through food.

Good sources of protein include:

Lean meats, fish, and eggs
Dairy products like Greek yogurt and cottage cheese
Plant-based options like beans, lentils, tofu, nuts, and seeds

Protein is vital for building and repairing muscle, maintaining lean mass during fat loss, and keeping you fuller longer. However, more isn’t always better—aim for balance and quality over excess.

Carbohydrates: Your Body’s Main Energy Source

Carbohydrates (or “carbs”) provide quick and efficient energy for your brain and muscles. There are two main types:

Simple carbs: sugars found in fruit, honey, and many processed foods
Complex carbs: starches and fibers found in vegetables, fruits, legumes, and whole grains

Complex carbs digest more slowly, helping regulate blood sugar and provide sustained energy.
While carbs often get a bad reputation, the right types—especially fiber-rich ones—are essential for health and performance.

Fats: Essential for Hormones and Energy

Despite their bad reputation, healthy fats are crucial for hormone balance, brain health, and long-term energy. Fats are more calorie-dense than protein or carbs, but they play important roles in your diet.

Common types include:

Healthy fats: monounsaturated, polyunsaturated, and omega-3 fats (found in olive oil, avocado, nuts, and fatty fish)
Unhealthy fats: trans fats and excessive saturated fats (found in processed and fried foods)

The Dietary Guidelines for Americans recommend avoiding trans fats entirely and keeping saturated fats below 10% of your daily calories. Replace them with healthier fats when possible.

Daily Calorie needs

Your daily calorie needs depend on your age, height, weight, activity level, and goal (lose, maintain, or gain weight).

This calculator uses two trusted formulas:

Mifflin–St Jeor Equation: estimates your Basal Metabolic Rate (BMR) based on height, weight, age, and gender.
Katch–McArdle Formula: uses lean body mass for a more precise result, especially for people who know their body fat percentage.

Once your BMR is calculated, it’s multiplied by an activity factor to determine your Total Daily Energy Expenditure (TDEE)—the total calories your body burns in a day.

For most adults:

Women typically need 1,600–2,400 calories/day
Men typically need 2,000–3,000 calories/day
These ranges increase with higher activity levels and decrease if you’re more sedentary.

How Macros Fit Into Your Daily Calories

Since carbs, protein, and fat provide nearly all of your body’s energy, your macro targets can be estimated from your daily calorie goal:

Protein: 4 calories per gram
Carbs: 4 calories per gram
Fat: 9 calories per gram

Your personalized macro split helps you reach your fitness goals—whether that’s building muscle, losing fat, or maintaining balance—and is based on evidence-based guidelines from sources like the American Dietetic Association, CDC, and World Health Organization.