How to Calculate Macros for Weight Loss: A Worked Example

Worked example

A hypothetical 40-year-old woman, 70 kg and 165 cm tall, with a desk job and little planned exercise (“sedentary or light”, × 1.53). She chooses a 500 kcal deficit and moderate protein (1.2 g/kg).

Result: about 1,600 kcal a day with 84 g protein, 197 g carbohydrate and 53 g fat. Rounded to the nearest 10 kcal, because the inputs are not precise enough for more. Her maintenance could reasonably be anywhere from 1,890 to 2,310 kcal, so the target is a starting point to adjust, not a fixed rule.

Step 1: Estimate resting energy

Resting energy is what your body uses at rest, for breathing, circulation and keeping warm. The Mifflin-St Jeor equation estimates it from weight, height, age and sex:

• Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
• Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5

It was developed in 1990 from measurements of 498 healthy adults aged 19–78, including people with obesity. A 2005 systematic review found it estimated resting metabolic rate within 10% of the measured value more often than the other common equations. It still misses by more than that for some people, and older adults and some ethnic groups were underrepresented in the research.

Step 2: Multiply by activity level

Total daily energy is resting energy multiplied by a physical activity level (PAL). The FAO/WHO/UNU expert report groups lifestyles into bands, with worked examples:

Pick the level that matches a typical week. Overestimating activity is one of the easiest ways to end up with a target that is too high. If you choose a higher level because you exercise, don’t also add exercise calories back on top.

Step 3: Choose a modest deficit

Taking 250 or 500 kcal a day off maintenance is a modest, transparent starting point. The NHS suggests aiming to lose 0.5 to 1 kg (1 to 2 lb) a week.

Don’t expect a fixed weekly loss. Research modelling energy balance shows weight change slows over time as the body adapts, so simple rules that turn a daily deficit into a set amount a week overstate long-term results.

Step 4: Set protein from body weight

Protein is usually set in grams per kilogram of body weight:

• 0.83 g/kg is EFSA’s population reference intake for adults, which covers the needs of nearly all healthy adults.
• 1.2–2.0 g/kg is the range sports bodies use for people who train regularly; the ISSN gives 1.4–2.0 g/kg for most exercising people.

Using current body weight can overstate protein at higher body weights. For more on protein, see Lesson 3: Protein or the Protein Calculator.

Step 5 and 6: Split the rest between fat and carbohydrate

EFSA’s reference ranges for adults are 20–35% of energy from fat and 45–60% from carbohydrate. Setting fat at 30% keeps it in the middle of its range; carbohydrate then fills the remaining calories.

Convert calories to grams with the standard factors used on EU food labels: 4 kcal per gram for protein and carbohydrate, 9 kcal per gram for fat (fibre is counted separately at 2 kcal/g). With higher protein, carbohydrate can fall below 45% of energy. That is a result of the arithmetic, not a recommendation to cut carbs. For the basics, read Lesson 4: Carbohydrates and Lesson 5: Dietary Fats.

Common mistakes

Using a goal weight. The equation was built from people’s actual weights, so use your current weight.

Treating the result as exact. It is an estimate with a margin of error. Your weight trend over several weeks tells you more than the equation.

Mixing raw and cooked weights when tracking. Rice, pasta and meat change weight when cooked. See raw vs cooked and how to read nutrition labels.

When not to calculate your own macros

Don’t use these steps if you are under 18, pregnant or breastfeeding, managing a medical condition with diet, taking medicine affected by what you eat, or have had an eating disorder. A doctor or registered dietitian can give advice that fits you.

Common questions