Macro Calculator

What is the Macro Calculator?

The macro calculator turns your body stats and a fitness goal into a clear daily eating target: how many calories to eat and exactly how many grams of protein, carbohydrate, and fat make up those calories. "Macros" is short for macronutrients — the three energy-providing nutrients in food. Counting calories alone tells you how much to eat; counting macros tells you what that food should be made of, which is what actually shapes muscle, energy, and body composition over time.

How to use it

1. Enter your sex, age, weight, and height. Toggle kg/lb and cm/in so you can type whatever your scale and tape measure show.
2. Pick your activity level, from sedentary to extra active, so the estimate reflects how much you actually move.
3. Choose a goal — lose fat, maintain, or build muscle — and the calculator adjusts your calories up or down for you.
4. Select a macro split preset, or choose Custom and drag the sliders to set your own protein, carb, and fat percentages.
5. Read your daily calories and macro grams instantly — there is no Calculate button — then copy the result and close the tab.

The formula and method behind it

The calculator runs four short steps in order:

BMR = 10 x kg + 6.25 x cm - 5 x age + s

First it finds your basal metabolic rate (the energy you burn at complete rest) with the Mifflin-St Jeor equation, where s is +5 for men and -161 for women. Then it scales that by an activity factor to get your total daily energy expenditure:

TDEE = BMR x activity factor

The activity factors are 1.2 (sedentary), 1.375 (light), 1.55 (moderate), 1.725 (very active), and 1.9 (extra active). Next it adjusts calories for your goal — a 20% deficit to lose fat, maintenance, or a 10% surplus to build muscle. Finally it splits those calories into grams, using 4 calories per gram for protein and carbohydrate and 9 calories per gram for fat:

grams = (calories x ratio percent) / kcal per gram

Examples

• Fat loss, balanced split: a 30-year-old man, 70 kg, 175 cm, moderately active. BMR is about 1649, TDEE about 2556, and a 20% cut gives roughly 2045 calories — about 153 g protein, 205 g carbs, and 68 g fat on a 30/40/30 split.
• Muscle gain, high-protein: a 28-year-old woman, 60 kg, 165 cm, very active. TDEE is about 2348, and a 10% surplus gives roughly 2583 calories — about 258 g protein, 258 g carbs, and 57 g fat on a 40/40/20 split.
• Keto maintenance: a 45-year-old man, 90 kg, 180 cm, sedentary at maintenance lands near 2148 calories — about 134 g protein, 27 g carbs, and 167 g fat on a 25/5/70 split.

Common use cases

• Setting up a meal-prep plan around a specific protein and calorie target.
• Switching from a balanced diet to low-carb or keto and seeing how the grams change.
• Dialing in a lean bulk or a cut without losing track of protein intake.
• Translating a coach's percentage split into concrete daily grams to log in an app.
• Sanity-checking whether your current diet has enough protein for the goal you are chasing.

Why use this one

Many macro tools lock you into a single preset or hide the math behind an account. This one gives you five ways to split your calories — balanced, low-carb, high-protein, keto, and a fully custom slider mode — and shows the grams update live as you drag. It handles both metric and imperial units, lays out BMR, TDEE, goal calories, and macros in one screen, and is built mobile first so it works one-handed. Best of all, it is completely private: every number stays in your browser, nothing is uploaded, and there is no app to install or login to create.

Frequently asked questions