What a macro calculator does
Macronutrients — “macros” for short — are the three nutrients that give your body energy: protein, carbohydrates and fat. Counting calories tells you how much you eat; setting your macros tells you where that energy comes from, which shapes your fullness, your training performance and how well you hold on to muscle.
This calculator takes your daily calories and splits them into grams of each macro based on the goal you pick. Everything runs in your browser — nothing is stored or sent anywhere.
How to use it
- Daily calories: type how many kilocalories you want to eat per day. If you don’t know the number yet, work it out first with a TDEE calculator.
- Macro split: choose a preset (Balanced, Low-carb, High-protein or Keto) or pick Custom to enter your own percentages.
- If you go custom, the tool checks that your percentages add up to 100% before it shows a result.
You’ll see the grams and kilocalories for protein, carbs and fat.
The formula: Atwater factors
We turn calories into grams using the Atwater factors, the standard used on nutrition labels:
- Protein: 4 kcal per gram
- Carbohydrates: 4 kcal per gram
- Fat: 9 kcal per gram
For each macro: macro kcal = calories × percentage ÷ 100, then grams = macro kcal ÷ kcal per gram.
Split presets
| Goal | Carbs | Protein | Fat |
|---|---|---|---|
| Balanced | 40% | 30% | 30% |
| Low-carb | 25% | 40% | 35% |
| High-protein | 40% | 40% | 20% |
| Keto | 5% | 25% | 70% |
Worked example
Someone eating 2000 kcal a day on a Balanced split (40% carbs, 30% protein, 30% fat):
- Protein: 2000 × 30 ÷ 100 = 600 kcal → 600 ÷ 4 = 150 g
- Carbs: 2000 × 40 ÷ 100 = 800 kcal → 800 ÷ 4 = 200 g
- Fat: 2000 × 30 ÷ 100 = 600 kcal → 600 ÷ 9 = 66.7 g
The kilocalories check out: 600 + 800 + 600 = 2000 kcal.
On a Keto split at 1800 kcal you’d get 112.5 g protein, 22.5 g carbs and 140 g fat. On High-protein at 2500 kcal: 250 g protein, 250 g carbs and 55.6 g fat.
Note: this calculator gives an informational estimate for educational purposes. It is not medical or nutritional advice. Talk to a health professional before changing your diet, especially if you have any condition.
Frequently asked questions
How much protein do I need per day?
A common target for active people is 1.6 to 2.2 g of protein per kilogram of body weight. The higher-protein presets (High-protein or Low-carb) make it easier to land in that range when you want to protect muscle during a calorie deficit.
Why does fat give fewer grams than carbs?
Because fat is more energy-dense: 9 kcal per gram versus 4 kcal for carbs and protein. For the same number of calories, a high fat percentage always works out to fewer grams.
Which macro split is best?
There is no single “best” split for everyone. The right one depends on your goal, activity and preferences. Protein usually stays high to preserve muscle, while the balance between carbs and fat is more flexible. Keto cuts carbs sharply; a balanced split works well for most people.
Do custom percentages have to add up to 100?
Yes. Because the three macros share 100% of your calories, their percentages must total exactly 100%. If they don’t, the tool warns you and holds the result until you fix the numbers.
Do I have to weigh my food to hit my macros?
Weighing your food for a few days early on helps you learn portion sizes; with practice you can eyeball it. Perfect precision isn’t required — getting close to your macros consistently matters far more than nailing them every single day.