Health
Macro Calculator
Work out a daily calorie target from your body stats and goal, then see it split into grams of protein, carbohydrate, and fat.
Calculation inputs
Heights and weights are in feet/inches and pounds.
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Estimates only, for general information. Not medical or nutritional advice.
About this calculator
This calculator estimates your daily calorie target from your body stats, activity level, and goal, then splits that target into grams of protein, carbohydrate, and fat. It is meant as a general planning starting point for people tracking food intake, not a medical or nutritional prescription.
How the calculation works
- BMR uses Mifflin-St Jeor: (10 × kg) + (6.25 × cm) − (5 × age) + 5 for men, −161 for women
- Maintenance calories = BMR × activity multiplier
- Lose weight applies a 20% deficit; gain weight applies a 15% surplus
- Protein and carbohydrate are 4 calories per gram, fat is 9 calories per gram
Notes and assumptions
Macro splits here are common starting points, not prescriptions — adjust based on how you feel and how your weight actually moves.
How it works in plain English
The calculator first estimates your basal metabolic rate (BMR), the calories your body burns at rest, using the Mifflin-St Jeor equation, which factors in your weight, height, age, and gender. That BMR is then multiplied by an activity multiplier ranging from sedentary to athlete, which scales it up to reflect the extra calories burned through daily movement and exercise, giving your maintenance calories.
Depending on your stated goal, the calculator adjusts maintenance calories by a set percentage: a 20% reduction for weight loss, no change for maintenance, or a 15% increase for weight gain. That adjusted number becomes your daily calorie target.
Finally, the target is divided among protein, carbohydrate, and fat using a percentage split that also depends on your goal, since different goals typically emphasize different macronutrient balances. Protein and carbohydrate both provide 4 calories per gram, while fat provides 9 calories per gram, so those calorie shares are converted into gram amounts using those conversion factors.
The formula
- BMR (Mifflin-St Jeor) = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5 (men) or -161 (women)
- Maintenance calories = BMR x activity multiplier
- Grams of protein or carbohydrate = (calories x share) / 4
- Grams of fat = (calories x share) / 9
Worked example
A 32-year-old man who is 5'9" and weighs 170 lb, moderately active (multiplier 1.55), aiming to maintain weight, converts to about 77.1 kg and 175 cm. His BMR works out to roughly 1,700 kcal, and multiplying by 1.55 gives a maintenance target of about 2,635 kcal.
With the maintenance split of 30% protein, 40% carbohydrate, and 30% fat, that comes to about 198 g of protein, 264 g of carbohydrate, and 88 g of fat per day.
If this same person switched his goal to weight loss instead, the calculator would apply a 20% reduction to the 2,635 kcal maintenance figure, bringing the daily target down to about 2,108 kcal. Weight-loss splits typically shift toward more protein, so at a 35% protein, 35% carbohydrate, and 30% fat split, that would work out to roughly 184 g of protein, 184 g of carbohydrate, and 70 g of fat per day, all recalculated from the lower calorie target.
Common activity level multipliers
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little to no exercise | 1.2 |
| Lightly active | Light exercise 1-3 days a week | 1.375 |
| Moderately active | Moderate exercise 3-5 days a week | 1.55 |
| Very active | Hard exercise 6-7 days a week | 1.725 |
| Athlete | Twice-daily training or physical job plus exercise | 1.9 |
Multipliers follow the widely used activity-factor approach applied to the Mifflin-St Jeor equation.
Frequently asked questions
How accurate is the calorie estimate?
The Mifflin-St Jeor equation is a widely used estimate, but it is still an approximation based on averages, and actual calorie needs vary with muscle mass, metabolism, and other individual factors. Treat the number as a reasonable starting point to adjust from based on how your weight actually changes over a few weeks.
Why do the macro percentages change with my goal?
The calculator applies a different protein, carbohydrate, and fat split depending on whether you selected weight loss, maintenance, or weight gain, since each goal commonly emphasizes macronutrients differently, such as higher protein for weight loss to help preserve muscle. These splits are general starting points, not fixed rules.
What if my actual results don't match the target?
Body weight changes depend on many factors beyond the formula, including hydration, activity outside the stated level, and day-to-day variation in intake. If your weight trend doesn't match your goal after a few consistent weeks, adjust the calorie target up or down rather than assuming the estimate was wrong.
Why is fat's calorie conversion different from protein and carbs?
Fat provides 9 calories per gram, more than double the 4 calories per gram that protein and carbohydrate each provide. This is a standard nutritional conversion, not something specific to this calculator, and it's why a small gram amount of fat can carry a relatively large share of total calories.
Should I follow this without talking to anyone?
This tool gives a general estimate for planning purposes and is not medical or nutritional advice. Anyone with health conditions, specific dietary needs, or concerns about a calorie or macronutrient plan should check with a qualified professional before making significant changes.