How to Calculate Your Macros: a step-by-step guide

"Counting macros" just means budgeting your food by its three energy-providing nutrients — protein, fat and carbohydrate — instead of only counting calories. Do it well and you can lose fat while keeping muscle, fuel your training, and stop guessing. The whole process is four steps of simple arithmetic, and this guide walks each one, then works a complete example that matches the Reckix TDEE & macro calculator exactly.

Step 1 — BMR with Mifflin-St Jeor

Your basal metabolic rate (BMR) is the energy your body burns at complete rest — just keeping you alive. The most reliable predictor for the general adult population is the Mifflin-St Jeor equation, which is why dietitians recommend it over older formulas like Harris-Benedict. It uses weight in kilograms, height in centimetres and age in years:

Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5

Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

The only difference between the two is the constant on the end: +5 for men, −161 for women. Working in imperial? Convert first — 1 inch = 2.54 cm and 1 lb = 0.4536 kg — then plug the metric numbers in.

Step 2 — activity multiplier to get TDEE

BMR is what you'd burn lying in bed all day. Real life adds walking, working and training, so you scale BMR up by an activity factor to reach your total daily energy expenditure (TDEE) — the calories you actually burn on a typical day:

TDEE = BMR × activity factor

Most desk-workers who train a few times a week land at moderate (×1.55). When in doubt, pick the lower factor — it's easy to overestimate activity, and you can always adjust from your real weight trend after a couple of weeks.

Step 3 — set a calorie target (cut / maintain / bulk)

TDEE is the number that holds your weight steady. To change your weight you nudge above or below it:

target = TDEE + goal adjustment

• Cut (lose fat): subtract about 500 kcal/day. On the classic 3,500 kcal ≈ 1 lb (0.45 kg) approximation, that's roughly a pound a week.
• Maintain: eat at TDEE, no adjustment.
• Lean bulk (gain muscle): add about 300 kcal/day for a slow, mostly-lean gain.

One safety rule: don't drive the target below about 1,200 kcal/day without medical supervision, because it becomes very hard to meet your nutrient needs. If a 500-calorie cut would take you under that floor, hold at 1,200 and lose more slowly instead. The 3,500 kcal ≈ 1 lb figure is a useful rule of thumb, not a law — real loss runs faster at first (water and glycogen) and slows as your body adapts.

Step 4 — split calories into gram targets

Now turn the calorie target into grams of each macro. First pick a percentage split, then convert using each macronutrient's energy density — the Atwater factors:

Protein = 4 kcal/g · Carbohydrate = 4 kcal/g · Fat = 9 kcal/g

The conversion for each macro is:

grams = target calories × percentage ÷ (4 for protein/carbs, or 9 for fat)

Common starting splits (protein / fat / carb):

• Balanced — 30 / 30 / 40: a flexible everyday default.
• High protein — 40 / 25 / 35: best for cutting or building muscle, because protein preserves lean mass and is the most filling macro.
• Low carb — 35 / 45 / 20: for people who feel better on fewer carbs.

Fat gets divided by 9 instead of 4, so a given percentage of calories buys you fewer grams of fat than of protein or carbs — that's why fat gram targets always look small next to the others.

A full worked example

Let's run the numbers for a 30-year-old man, 175 cm, 75 kg, moderately active, aiming to lose fat on a balanced 30/30/40 split — the same profile the calculator starts with, so you can check every figure against the live tool.

1. BMR

10 × 75 + 6.25 × 175 − 5 × 30 + 5 = 750 + 1,093.75 − 150 + 5 = 1,699 kcal

2. TDEE

1,698.75 × 1.55 ≈ 2,633 kcal — his maintenance calories.

3. Calorie target (cut)

2,633 − 500 = 2,133 kcal/day. That's above the 1,200 floor, so it stands.

4. Macro grams (30 / 30 / 40)

So his daily plan is roughly 2,133 kcal · 160 g protein · 71 g fat · 213 g carbs. Spread over four meals that's about 533 kcal and 40 g of protein each. Every one of those numbers matches the calculator's output for the same inputs — because the guide and the tool use the identical formulas.

Making it stick

1. Prioritise the protein number. If you track only one macro, track protein — roughly 1.6–2.2 g per kg of body weight protects muscle and controls hunger, in a cut or a bulk.
2. Weigh the trend, not the day. Bodyweight bounces with water and food volume. Judge progress on a 2–4 week average, then adjust calories if the trend isn't moving.
3. Recalculate as you change. BMR falls as you lose weight, so a target that created a deficit at 90 kg may only maintain at 80 kg. Re-run the numbers every 4–5 kg.
4. Stay flexible on fat and carbs. Once protein and total calories are set, the exact fat/carb balance is mostly personal preference — pick the split you can adhere to.

Methodology & sources

The formulas in this guide are exactly those used by the Reckix TDEE & macro calculator: the Mifflin-St Jeor BMR equation, the standard 1.2–1.9 activity multipliers, a goal adjustment (−500 to cut, +300 to gain) floored at 1,200 kcal/day, and the Atwater energy factors (protein and carbohydrate 4 kcal/g, fat 9 kcal/g). Method cross-checked against Mifflin et al. (1990) and the Academy of Nutrition and Dietetics' comparison of predictive equations; the 3,500 kcal ≈ 1 lb figure is a widely used approximation, not a precise law. All figures are directional, as of July 2026, and individual needs vary — adjust against your real weight trend.