Macro calculator

How this calculator works

Three steps, in this order, because each one depends on the last.

1. Your maintenance calories

First it estimates the energy your body burns at complete rest, using the Mifflin St Jeor equation, which is the most accurate of the common formulas for people who are not extremely lean or extremely heavy. Then it multiplies that by an activity factor between 1.2 and 1.9 to cover everything you do on top of lying still. The result is your maintenance: eat that and, roughly speaking, your weight holds.

2. The adjustment for your goal

Losing fat sets your target about 20% below maintenance, which for most people lands between 300 and 600 calories a day. That is aggressive enough to show on the scale within a few weeks and gentle enough that you can still train, sleep and think. Building sets it about 10% above, because a bigger surplus mostly buys you fat. Maintaining leaves it alone.

3. The split

Protein comes first and is set from your body weight, not from a percentage, because your muscle does not know how many calories you are eating. Fat takes a share of the total, never dropping so low that it causes problems. Carbs get whatever is left, which is why the carb number moves most when you change anything else. If you want to read the reasoning in full, the macro tracking guide covers it.

What to actually do with these numbers

A target you never check is a wish. The gap between people who hit their macros and people who do not is almost never knowledge, it is whether logging costs two minutes or ten. So:

• Chase protein, approximate the rest. Protein holds onto muscle in a deficit and is the most filling of the three. Carbs and fat can wander by 20 g without changing your week.
• Judge it on the weekly average. Daily weight swings a kilo or more on water alone, which is a whole separate thing worth understanding. Three or four weeks of averages tell you whether the target is right.
• Recalculate as you change. Maintenance falls as you get lighter. Come back every four to six kilos.
• Log the days you would rather not. Those are the days carrying the information.

Sources

• A new predictive equation for resting energy expenditure in healthy individuals (Mifflin St Jeor), American Journal of Clinical Nutrition, 1990
• Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults, Journal of the American Dietetic Association, 2005
• Human energy requirements: report of a joint FAO, WHO and UNU expert consultation, Food and Agriculture Organization, 2004
• International Society of Sports Nutrition position stand: protein and exercise, Journal of the International Society of Sports Nutrition, 2017
• Food energy: methods of analysis and conversion factors, Food and Agriculture Organization, 2003

How this was made

Written by Abdullah Javaid, founder of Calfit, drafted with AI assistance and edited by hand. Maintenance is the Mifflin St Jeor equation multiplied by an activity factor between 1.2 and 1.9, and the target is 20% under for fat loss or 10% over for building. Protein is set from body weight, fat takes 25% of calories on a cut, and carbs take the rest, at 4, 4 and 9 kcal per gram.

Quick questions