Macro calculator

A macro calculator turns your daily calorie needs into grams of the three macronutrients — protein, fat, and carbohydrates. Calorie targets alone are hard to act on at the grocery store; nutrition labels list grams. Converting your target into grams of each macronutrient is what lets you plan a real plate of food, compare two products, and tell whether a day actually hit the mark.

What each macronutrient does

All three supply energy, but they are not interchangeable. Protein is the structural one: it provides amino acids your body uses to repair and build muscle, and it is the most filling of the three per calorie, which is why a higher-protein day tends to feel less hungry. Fat is the most energy-dense at 9 calories per gram, and a baseline amount supports hormone production and the absorption of vitamins A, D, E, and K. Carbohydrates are the body's quickest fuel and the main energy source for hard exercise; they are also where fibre comes from. The split this tool uses keeps all three in meaningful amounts rather than cutting any to zero.

How this calculator works

It starts with the Mifflin-St Jeor equation, a well-tested formula that estimates the calories your body burns at rest from your weight, height, age, and sex. Multiplying that by your activity level gives your total daily calories — your TDEE. Your goal then adjusts the target: maintain keeps it as is, lose subtracts 500 calories a day, and gain adds 500. Finally the calories are split 30% protein, 30% fat, and 40% carbs and converted to grams at 4 calories per gram for protein and carbs and 9 for fat.

A worked example

Take a 30-year-old man who weighs 80 kg, is 180 cm tall, and trains a few times a week (the moderate activity level). His resting burn is about 1,780 calories; at moderate activity that becomes roughly 2,759 calories a day. To maintain weight, the 30/30/40 split works out to about 207 g of protein, 92 g of fat, and 276 g of carbs. You can sanity-check it: 207 g protein and 276 g carbs at 4 calories each plus 92 g fat at 9 calories add back up to about 2,760 calories.

Switch the goal to lose and the target drops to 2,259 calories, which rescales the same split to roughly 169 g protein, 75 g fat, and 226 g carbs. For comparison, a 30-year-old woman of 65 kg and 165 cm at the light activity level lands near 1,884 calories to maintain — about 141 g protein, 63 g fat, and 188 g carbs. The grams always move together because the percentages stay fixed; only the calorie total changes.

Reading and using the split

• Protein and carbs provide 4 calories per gram; fat provides 9. That is why fat grams look small next to carb grams even when both supply 30% of calories.
• The 500-calorie change is a common rule of thumb for losing or gaining at a steady pace rather than an extreme one. Roughly speaking it points toward about half a kilo of weight change a week.
• You rarely hit the grams exactly. Getting within 10 to 15 grams of each, especially protein, is close enough for the numbers to do their job.
• The 30/30/40 ratio is a balanced default, not a rule. Low-carb and keto eating shifts calories from carbs toward fat; some strength athletes push protein higher and carbs lower. If you change the ratio, the calorie total stays the same — you are only moving where those calories come from.
• Real needs vary with body composition, training, sleep, and health, so treat the output as a starting point you adjust based on how your weight and energy actually respond over a few weeks.

Frequently asked questions

Last reviewed June 2026. Calories use the Mifflin-St Jeor equation. For general guidance, not medical or dietary advice.