Macro Calculator

The macro calculator turns basic body and lifestyle inputs into a daily calorie target, then splits that target into protein, fat, and carbohydrate grams. It is built for adults who want a reproducible starting point for nutrition tracking: enter age, sex, height, weight, activity level, a goal, and a protein preference, and the calculator shows the full chain from resting energy to grams.

What the result tells you

The primary result is daily calories. Beneath it, the calculator shows:

• Protein in grams — your chosen g/kg target times body weight.
• Fat in grams — 25% of the calorie target.
• Carbs in grams — the remaining calories.
• Estimated BMR — resting energy expenditure from the Mifflin-St Jeor equation.
• Estimated TDEE — BMR times the activity multiplier, before the goal adjustment.

The result is an estimate to start from, not a prescription. Track actual scale, energy, and performance trends before committing to a number for weeks.

How it works

The calculation runs in three stages.

1. Resting energy. The Mifflin-St Jeor equation predicts resting energy expenditure from age, sex, height, and weight. It was derived from indirect calorimetry measurements in healthy adults and is one of the most commonly used resting-energy equations. The resting energy expenditure calculator and the BMR calculator apply the same equation family if you want to explore it directly.

2. Activity and goal. A standard activity multiplier (1.2 for sedentary up to 1.9 for very active) converts resting energy into an estimated total daily expenditure. The goal then adjusts the total: −15% for losing, +0% for maintaining, +15% for gaining. The ACSM position stand on weight loss calls for an energy deficit of 500–1,000 kcal/day for adults, so check whether your −15% figure lands in that range — for some body sizes it will be smaller.

3. Macro split. Protein grams are set directly by your target: the default 1.6 g/kg sits inside the 1.4–2.0 g/kg/day range the ISSN position stand recommends for most exercising adults. Protein and carbs are counted at 4 kcal per gram and fat at 9 kcal per gram. Fat is fixed at 25% of calories, a middle-ground split inside the adult acceptable range of 20–35% of calories.

Formula

The Mifflin-St Jeor equations:

$\text{BMR} = 10 \times \text{weight kg} + 6.25 \times \text{height cm} - 5 \times \text{age} + 5 \quad (\text{male})$

$\text{BMR} = 10 \times \text{weight kg} + 6.25 \times \text{height cm} - 5 \times \text{age} - 161 \quad (\text{female})$

Daily calories:

$\text{calories} = \text{BMR} \times \text{activity factor} \times \text{goal factor}$

Macro grams:

$\text{protein g} = \text{protein target (g/kg)} \times \text{weight kg}$

$\text{fat g} = \frac{0.25 \times \text{calories}}{9}$

$\text{carb g} = \frac{\text{calories} - 4 \times \text{protein g} - 0.25 \times \text{calories}}{4}$

Worked example

Take the defaults: a 30-year-old male, 175 cm, 70 kg, moderate activity, maintaining weight, protein target 1.6 g/kg.

BMR:

$\text{BMR} = 10 \times 70 + 6.25 \times 175 - 5 \times 30 + 5 = 1648.75$

TDEE with the moderate factor of 1.55:

$\text{TDEE} = 1648.75 \times 1.55 = 2555.5625$

Maintaining keeps the total unchanged, so daily calories are 2,556 kcal (rounded). Protein is:

$1.6 \times 70 = 112\text{ g}$

Fat is 25% of calories:

$\frac{0.25 \times 2555.5625}{9} = 70.99 \approx 71\text{ g}$

Carbs absorb the rest:

$\frac{2555.5625 - 448 - 638.89}{4} = 367.17 \approx 367\text{ g}$

The calculator displays 2,556 kcal — 112 g protein, 71 g fat, 367 g carbs.

How to choose your inputs

Be honest about activity level; people consistently overestimate it, and the multiplier changes calories by hundreds. The “moderate” option assumes intentional exercise three to five days a week on top of a mostly desk-based day. Pick the protein target by your situation: around the 1.4 g/kg end for light training, toward 2.0 g/kg for serious muscle-building programs, and the DRI population reference of 0.8 g/kg applies to sedentary adults — see the protein calculator for that comparison.

For the goal, a −15% cut is a modest, sustainable starting deficit; a +15% surplus is a common starting point for gaining. Reassess every few weeks: if the scale moves faster or slower than intended, adjust by 100–200 kcal rather than overhauling the whole plan. The meal calorie calculator helps you count actual meals against the gram targets.

Limitations and disclaimer

Every number here is an estimate. The Mifflin-St Jeor equation predicts resting energy for populations; individual metabolism varies, activity multipliers are coarse conventions, and tracking error in portions and labels is normal. The result is not medical or nutritional advice and is not appropriate as a clinical plan for diabetes, kidney or liver conditions, pregnancy, an eating disorder history, or athletes with coached nutrition programs. A registered dietitian or clinician should individualize any sustained calorie or macro plan.

Common mistakes

• Treating the calorie target as a measured fact instead of a starting estimate.
• Overstating activity level and then wondering why weight is not changing as predicted.
• Forgetting that protein grams stay fixed while fat and carbs rescale when the goal changes.
• Counting protein and carbs at 4 kcal/g and fat at 9 kcal/g inconsistently when cross-checking by hand.
• Ignoring the deficit check: a small person’s −15% may fall well below the 500–1,000 kcal/day deficit ACSM describes for weight loss.

Sources

• Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO, A new predictive equation for resting energy expenditure in healthy individuals, The American Journal of Clinical Nutrition 1990;51(2):241–247, PMID 2305711 — the Mifflin-St Jeor resting energy equations used here.
• Jäger R, Kerksick CM, Campbell BI, et al., International Society of Sports Nutrition Position Stand: protein and exercise, J Int Soc Sports Nutr 2017;14:20 — the 1.4–2.0 g/kg/day protein range for most exercising adults.
• Donnelly JE, Blair SN, Jakicic JM, et al., ACSM Position Stand: Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults, Med Sci Sports Exerc 2009;41(2):459–471, PMID 19127177 — the 500–1,000 kcal/day energy deficit for adult weight loss.
• Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids, 2005, DOI 10.17226/10490 — adult acceptable macronutrient distribution ranges (fat 20–35%, protein 10–35%, carbohydrate 45–65% of calories).