What is the Macro Calculator and what does it do?

The Macro Calculator is a tool designed to determine your optimal daily intake of macronutrients—proteins, carbohydrates, and fats—based on your personal goals, such as weight loss, muscle gain, or maintenance. It uses inputs like your age, sex, weight, height, activity level, and goal to calculate your total daily energy expenditure (TDEE) and then breaks that down into specific gram amounts for each macro, ensuring a balanced and sustainable approach to nutrition.

How is the macro calculation different from a standard calorie calculator?

While a standard calorie calculator only gives you a single number for daily calories, the Macro Calculator goes a step further by distributing those calories into the three macronutrient groups, which is crucial because each macro plays a unique role in your body—protein supports muscle repair, carbs fuel energy, and fats aid hormone function. This detailed breakdown allows you to tailor your diet more precisely, especially for athletic performance or body composition changes, rather than just focusing on total energy intake.

What information do I need to provide to get accurate results from the Macro Calculator?

To get accurate results, you'll need to input your biological sex, age, current weight, height, and your typical daily activity level (ranging from sedentary to very active), as these factors directly influence your basal metabolic rate and overall energy expenditure. Additionally, you must specify your primary goal—whether it's losing fat, building muscle, or maintaining your current weight—because the calculator adjusts your calorie surplus or deficit and then sets macro ratios accordingly, such as higher protein for muscle gain or lower fat for cutting.

Can I use the Macro Calculator for meal planning, and how often should I recalculate my macros?

Yes, the Macro Calculator is highly useful for meal planning, as once you have your daily macro targets, you can divide them across your meals and snacks, and even adjust the settings to calculate per-meal macros if you eat a set number of times per day. You should recalculate your macros every 2 to 4 weeks, or whenever your weight changes by more than 5 to 10 pounds, because your TDEE changes as your body composition shifts, and also if you significantly change your activity level, such as starting a new exercise routine, to keep your numbers accurate and effective.

Macro Calculator

Last updated: 2026-10-01

Macro Calculator — Calculates daily maintenance calories and macronutrient targets based on weight and exercise.

Inputs

Result

Enter values and press Calculate

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Common Examples — Click to Fill

	Weight (kg)	Exercise hours	target
Child	35	1.5	—
Teen	52.5	2.25	—
Adult (F)	70	3	—
Adult (M)	105	4.5	—
Elderly	140	6	—

TL;DR: To calculate your macros, use the formula Calories Maintenance = (10 × weight in kg) + (6.25 × height in cm) – (5 × age) + 5 (men) or –161 (women) + (6 × exercise hours per week), then set protein at 2g per kg of body weight, fat at 1g per kg, and fill remaining calories with carbohydrates — for a 70 kg person doing 3 hours of weekly exercise aiming to maintain, this equals roughly 2,255 calories, 140g protein, 70g fat, and 262g carbs.

What Is the Macro Calculator?

The Macro Calculator is a free online tool that estimates your daily energy expenditure (maintenance calories) and then breaks that number into three macronutrient targets: protein, fats, and carbohydrates. It does not track food, weigh portions, or connect to an app — it simply gives you the starting numbers you need for a structured diet.

This calculator is for anyone who wants to stop guessing and start measuring. Whether you are trying to lose fat, build muscle, or simply maintain your current weight and body composition, knowing your daily calorie and macro targets is the foundation. Athletes, recreational gym-goers, and even people managing conditions like diabetes or PCOS can use macro targets to stabilise blood sugar, improve satiety, and feel more energetic throughout the day.

Unlike generic online calculators that ask for obscure inputs like body fat percentage or activity multipliers, this tool uses just three inputs — body weight, weekly exercise hours, and your goal — making it accessible to beginners while still being accurate enough for serious tracking.

How to Use the Calculator

Follow these steps to get your complete macro breakdown in under thirty seconds:

Enter your body weight (peso_kg): Type your current weight in kilograms. If you know your weight in pounds, divide it by 2.2 to get kilograms. For example, 154 lbs ÷ 2.2 = 70 kg.
Enter your weekly exercise hours (ejercicio_hrs): Add up all deliberate exercise you did in the last seven days — this includes gym sessions, running, cycling, team sports, or even brisk walking if it was sustained for 30+ minutes. Do not include daily walking to work or household chores.
Choose your target (target): Select one of the three goals: mantener (maintain current weight), perder (lose fat), or ganar (build muscle). If you select a loss or gain goal, the calculator will adjust your calories by a fixed deficit or surplus.
Click Calculate: The tool will process your inputs and display your maintenance calories, then break them into protein, fat, and carbohydrate gram targets.

That is the entire workflow. There are no hidden settings, no advanced toggles, and no requirement to know your body fat percentage. If you can type a number and press a button, you can use this calculator.

Formula and Calculation Method

The calculator uses a modified Mifflin-St Jeor equation, which is one of the most validated formulas for estimating basal metabolic rate (BMR) — the calories you burn at complete rest. The formula then adds an activity factor based on your exercise hours per week.

The full formula for maintenance calories is:

Calories Maintenance = (10 × weight_kg) + (6.25 × height_cm) – (5 × age) + 5 (for men) or –161 (for women) + (6 × exercise_hours_per_week)

If you selected perder or ganar, the calculator applies a 15–20% adjustment to this base number. For maintenance, no adjustment is made.

Once maintenance calories are established, the macro split is calculated as follows:

Protein: 2 grams per kilogram of body weight (2 × weight_kg), which preserves muscle mass and promotes satiety.
Fat: 1 gram per kilogram of body weight (1 × weight_kg), which supports hormone production and cellular function.
Carbohydrates: Remaining calories. The calculator subtracts protein calories (protein × 4) and fat calories (fat × 9) from total calories, then divides the remainder by 4 to get carbohydrate grams.

Worked example with real numbers:

Imagine a 30-year-old man who weighs 70 kg, is 175 cm tall, exercises 3 hours per week, and wants to maintain weight. Here is the step-by-step calculation:

BMR component: (10 × 70) + (6.25 × 175) – (5 × 30) + 5 = 700 + 1093.75 – 150 + 5 = 1,648.75 calories
Activity adjustment: 6 × 3 hours = 18 calories
Maintenance calories: 1,648.75 + 18 = 1,666.75 calories (rounded to 1,667)
Protein: 2 × 70 = 140 g (560 calories)
Fat: 1 × 70 = 70 g (630 calories)
Remaining calories for carbs: 1,667 – 560 – 630 = 477 calories ÷ 4 = 119 g carbs

This example gives a final macro breakdown of 1,667 calories, 140g protein, 70g fat, and 119g carbohydrates. Note that if your height and age differ, the calorie number will shift accordingly, but the macro split remains proportional to body weight.

Practical Examples

To see how the calculator behaves across different profiles, here are three realistic scenarios. All examples assume the user is 30 years old and 170 cm tall (unless stated otherwise), and uses the mantener target.

Scenario	Weight (kg)	Exercise (hrs/week)	Maintenance Calories	Protein (g)	Fat (g)	Carbs (g)
Sedentary woman	60	0	1,441	120	60	121
Active man	90	6	2,314	180	90	214
Lean endurance athlete	65	10	1,991	130	65	226

In the first scenario, the sedentary woman has very few carbs because her total calorie budget is low — this is expected. In the second, the active man has a high protein target because his body weight is higher, and his carbs are moderate because his maintenance calories are high. In the third, the endurance athlete’s carbs are proportionally higher relative to their calorie total, which supports glycogen replenishment for frequent training.

The key takeaway from these examples is that protein and fat are determined by body weight, while carbs are the flexible variable that fills the remaining space. If you have a low calorie target, carbs will drop; if you exercise more and eat more, carbs rise.

Tips for Accurate Results

Your results are only as reliable as the numbers you enter. Here are five specific tips to maximise accuracy:

Weigh yourself in the morning, fasted: Your weight can fluctuate by 1–2 kg throughout the day due to water, food, and glycogen. Always enter your morning weight after using the bathroom and before eating or drinking.
Convert pounds correctly: If you weigh yourself in pounds, divide by 2.2 (not 2.0). A 150 lb person is 68.2 kg, not 75 kg. This error alone would shift your protein target by 14 grams.
Count only deliberate exercise: Walking to the bus stop or standing at work does not count. Only log sessions where your heart rate was elevated for a sustained period — weightlifting, running, swimming, HIIT, or a fitness class.
Be honest with the target selector: If you select perder, the calculator will create a deficit. If you are already lean and want to gain muscle, ganar is correct. Choosing mantener when you actually want to lose fat will result in a zero-calorie adjustment, and you will not see weight change.
Recalculate every 5 kg of weight change: Because protein and fat are tied directly to body weight, losing 5 kg will lower your protein target by 10 grams and your fat by 5 grams. Re-run the calculator monthly or after any significant weight shift.

Common mistakes to avoid: Do not enter negative values or zero for weight — the formula cannot work with these. Do not confuse kg with pounds; the calculator expects metric units. Also, avoid entering more than 20 hours of exercise per week unless you are a professional athlete, as the activity multiplier becomes unrealistic for most people.

Frequently Asked Questions

How accurate is the Macro Calculator compared to lab testing?

This calculator uses the Mifflin-St Jeor equation, which is accurate to within about 10% of your true resting metabolic rate. That means if it says your maintenance is 2,000 calories, your actual maintenance could be anywhere from 1,800 to 2,200 calories. Lab testing (like indirect calorimetry) is more precise, but this free method is sufficient for most people. Track your weight for two weeks using these macro targets; if you are not maintaining, adjust your intake by 100–150 calories per day and re-assess.

Do I need to hit all three macros every single day?

No. Your protein target is the most important — aim to hit it daily because it preserves muscle mass and keeps you full. Your fat target is a minimum, not a maximum, so going slightly over is fine, especially if you eat nuts, olive oil, or fatty fish. Carbs are the most flexible; you can vary them by 20–30 grams daily without consequences, as long as your weekly calorie average matches your target. The calculator gives you numbers, but real life involves meals out, travel, and social events — aim for consistency over perfection.

What if I want to lose weight — should I change my macros manually?

No, you should not. If you select the perder target, the calculator automatically reduces your maintenance calories by 15–20%, which typically results in a 300–400 calorie deficit. That is the recommended range for sustainable fat loss without sacrificing muscle. If you manually cut carbs further, you will likely feel lethargic and hungry, and you risk losing muscle mass. Use the calculator's built-in deficit first. If after three weeks your weight has not dropped, reduce total calories by 150 per day, not by eliminating an entire macro group.