Macro Calculator: Protein, Carbs and Fat for Your Goal

How the macro calculator works

Macros, short for macronutrients, are the three things in food that carry calories: protein and carbohydrate at about 4 calories per gram, fat at about 9. The calculator works in four steps, and each one hands its number to the next.

1. Resting burn. The Mifflin-St Jeor equation estimates the calories you burn lying still all day. Men: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. Women: the same, but − 161 at the end.
2. Maintenance. Resting burn × an activity multiplier, from 1.2 for a desk job to 1.9 for hard training plus a physical job. This is roughly what you eat to stay the same weight.
3. Target. To lose fat, maintenance minus 2.5 kcal per pound of bodyweight (about 0.5% of your weight a week), never more than 500 a day. Unchanged to maintain, or plus 250 for a lean gain. A deficit never takes the target below 1,200 kcal for women or 1,500 for men; if maintenance is already within 100 kcal of that floor, no deficit is suggested at all.
4. Split. Protein first, by bodyweight. Fat second, as a share of calories. Carbs fill the rest.

Steps one to three are the calorie calculator; if you only want the calorie number and the reasoning behind each activity level, start there. This page adds step four.

A worked example

The calculator's default: a woman, 35, 160 lb (72.6 kg), 5 ft 5 in (165.1 cm), training three to five days a week, losing fat.

The 400 kcal deficit is aimed at about 0.8 lb (0.36 kg) a week. The split works out to 32% protein, 43% carbs and 25% fat: about 36 g of protein, 48 g of carbs and 13 g of fat at each of four meals.

The rules behind each macro

Protein is highest when cutting. Morton and colleagues (2018) pooled 49 lifting studies and found muscle gains leveled off around 1.6 g/kg a day, with possible benefit up to 2.2. In a deficit the body has more reason to break muscle down, and reviews of dieting lifters, such as Helms and colleagues (2014), put protein higher there. In a surplus the extra calories spare protein, so 1.6 is enough. The protein calculator lets you set this one number by itself, and the protein guide covers the research in full.

Protein is capped at 35% of calories. That is the top of the Acceptable Macronutrient Distribution Range set by the US Institute of Medicine. It kicks in for heavier people with a lot of body fat, where grams per kilogram of total weight overshoots, and for some smaller, less active women whose target sits at the 1,200 kcal floor.

Fat never drops below 0.6 g/kg (0.27 g/lb). Fat carries vitamins A, D, E and K, and very low-fat diets are linked to lower testosterone in men. The 25 to 30% band sits inside the Institute of Medicine's 20 to 35% range for adults.

Carbs get the rest because they fuel hard training and they are the macro with the most room to move. For the people this calculator is built for, carbs land between about 40 and 55% of calories.

What changes your macros

• Bodyweight. The biggest lever. Each extra 10 lb (4.5 kg) adds about 45 kcal to resting burn, roughly 70 kcal to maintenance at moderate activity, and 9 g of protein when cutting.
• Activity. Moving from training 1 to 3 days a week to 3 to 5 days adds about 13% to maintenance: about 250 kcal for someone maintaining on 2,000. Most of that goes to carbs.
• Age. Five fewer calories of resting burn a day for every year. Between 30 and 60 that is 150 kcal, or about 230 at maintenance with moderate activity: one small snack. Muscle you keep by lifting matters more than the birthday; strength training over 50 covers why.
• Sex. The equation's constant differs by 166 kcal at the same height, weight and age. Protein per kilogram does not change.
• Goal. Switching from losing fat to building muscle moves the target by the deficit plus 250, usually 550 to 750 kcal, and drops protein from 2.0 to 1.6 g/kg. Most of the difference lands in carbs, the rest in fat: for the default example, 650 kcal more becomes 119 g more carbs and 32 g more fat.

How accurate it is

Mifflin-St Jeor was built in 1990 from measured resting burn in 498 healthy adults. A 2005 systematic review by Frankenfield and colleagues found it the most reliable of the common equations, landing within 10% of measured resting burn in more people than the alternatives. Within 10% still means a 1,500 kcal estimate could really be 1,350 or 1,650.

The activity multiplier adds more error than the equation. People tend to rate themselves one level too active, and one level is worth about 200 to 350 kcal. If you lift three times a week and sit the rest of the day, "Train 1–3 days/week" is usually the honest pick, even with a fourth session some weeks.

Things the formula cannot see: how much of your weight is muscle, daily steps, sleep, medications, thyroid conditions, and menstrual cycle swings in water weight. Treat the result as a first guess that your scale will correct. The 3,500-calories-per-pound rule behind the weekly loss estimate is also a rough average; loss usually runs faster in the first weeks and slows as you get lighter.

Using your macros day to day

1. Track for two weeks, honestly. Weigh food in grams for the first fortnight; eyeballed portions run low. After that most people can estimate.
2. Build each meal around protein. 30 to 40 g of protein per meal, four meals, covers most targets. High-protein, low-calorie foods make that easier in a deficit, and a 100 g protein meal plan shows a full day.
3. Put carbs near training. A carb-heavy meal 1 to 3 hours before lifting and another after is a sensible default. It is a preference, not a rule; the daily total matters more.
4. Let fat and carbs trade. Ten grams of fat equals about 22 grams of carbs. If dinner runs fat-heavy, eat fewer carbs at it. Calories and protein stay fixed.
5. Judge by the weekly average. Weigh in each morning, average the week, and compare weeks. Single days swing 2 to 4 lb (1 to 2 kg) on water and salt alone.

When to change your numbers

After two to three weeks at the same target, compare your weekly averages.

Change one thing at a time, by small steps, and leave protein alone. After 8 to 12 weeks of dieting, a week or two at maintenance makes the next phase easier to stick to. Cutting without losing muscle covers the training side of a deficit, and body recomposition explains when maintenance calories are the better choice.

Questions people ask

What macros should I eat to lose weight?

For most people who lift: 2.5 kcal per pound of bodyweight under maintenance (500 at most), protein at 2.0 g/kg (0.9 g/lb), fat at 25% of calories, carbs for the rest. That typically lands near 30% protein, 45% carbs and 25% fat.

What macros should I eat to build muscle?

About 250 kcal over maintenance, protein at 1.6 g/kg (0.7 g/lb), fat at 30%, carbs for the rest. A bigger surplus mostly adds fat, not faster muscle.

Is 40/30/30 a good macro split?

It works for many people, but a fixed ratio scales badly. At 3,000 kcal, 30% protein is 225 g, more than most need; at 1,500 kcal it is 113 g, which may be short for a heavier lifter. Setting protein by bodyweight avoids both.

Do I have to hit my macros exactly?

No. Within about 100 kcal of the target and 10 g of protein, on most days, is on target. The weekly average is what moves the scale.

Should I count macros or just calories?

Calories plus protein is enough for most people. Tracking carbs and fat separately helps if you are curious about your energy in training, or if one of them keeps crowding out protein.

Can I eat low-carb with these numbers?

Yes. Keep calories and protein, then move calories from carbs to fat. Fat loss depends on the calorie total, not the carb share, though many lifters find hard sessions feel worse with very few carbs.

Do macros change with age?

Calories drop slightly with age; protein needs, if anything, go up. Older adults often do better near the top of the protein range and spread it evenly over three or four meals.

Where these numbers come from

The resting-burn equation is Mifflin, St Jeor and colleagues, A new predictive equation for resting energy expenditure in healthy individuals (American Journal of Clinical Nutrition, 1990). The accuracy comparison is Frankenfield, Roth-Yousey and Compher, Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review (Journal of the American Dietetic Association, 2005). The activity multipliers are the standard factors used with these equations. Protein targets follow Morton and colleagues, A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults (British Journal of Sports Medicine, 2018), and Helms, Aragon and Fitschen, Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation (Journal of the International Society of Sports Nutrition, 2014). The 35% protein cap and the 20 to 35% fat range are the Institute of Medicine's Acceptable Macronutrient Distribution Ranges, from its Dietary Reference Intakes for energy and macronutrients (2005). The calorie floors, the 0.6 g/kg fat minimum and the adjustment table are our own conservative rules.

This calculator is for healthy adults. It is not medical advice; if you have a medical condition or take medication that affects appetite or weight, set your targets with a doctor or registered dietitian.