How to calculate your calories and macros (the Mifflin-St Jeor method)

Updated: June 14, 2026

Before you worry about a single meal, you need two numbers: how many calories to eat each day, and how to split them across protein, carbs and fat — your "macros." That's exactly what Kaizmax works out for you in 2 minutes, but it pays to understand the mechanics. Once you know where these numbers come from, you also know what to tweak when the scale stalls.

We'll use the Mifflin-St Jeor formula, the modern reference for estimating energy expenditure. It's the same one coded into the app, step by step.

Step 1 — Your basal metabolic rate (BMR)

Your basal metabolic rate is the energy your body burns at complete rest, just to stay alive (breathing, pumping blood, holding temperature). Mifflin-St Jeor estimates it from your weight, height, age and sex:

Example: a 30-year-old woman, 168 cm, 65 kg → 10 × 65 + 6.25 × 168 − 5 × 30 − 161 = 1,389 kcal. That's your theoretical floor: what you'd burn lying in bed all day.

Step 2 — The activity factor (TDEE)

Nobody lies in bed all day. So we multiply BMR by an activity factor that reflects your daily life outside training (work, commuting, walking). That turns BMR into TDEE — your total daily energy expenditure.

Kaizmax then adds your training sessions on top, instead of burying everything in a single factor: each session counts for roughly 60 min × 0.07 × weight, spread across the week. The result: train 4 times or 0 times and your calorie total changes — logical, and more precise than one fixed multiplier.

Step 3 — The goal adjustment

Your TDEE is maintenance. To move the needle, you apply an offset:

Why −20% and not −40%? Because a brutal deficit makes you lose muscle, slows your metabolism and becomes impossible to sustain. Slow and steady wins.

Step 4 — The safety floors

Whatever the maths says, Kaizmax never drops below a minimum: 1,500 kcal for men, 1,200 kcal for women. Below that it becomes nearly impossible to cover your micronutrient needs, and your body shifts into conservation mode. If your calculation lands lower, we pull it back up to the floor.

Step 5 — Splitting the macros

Once the calorie total is set, we cut it into three. Order matters: protein is protected first, then fat, and carbs fill the rest.

Protein

It repairs and builds muscle, and it's the most filling macro. Aim for 2.0 g per kg of body weight when cutting (to preserve muscle in a deficit) and 1.8 g/kg otherwise, capped at 230 g. At 4 kcal per gram.

Fat

Essential for hormones and vitamin absorption. We take the greater of 28% of calories or 0.6 g/kg of body weight, never dropping too low. At 9 kcal per gram.

Carbs

Your training fuel. They take whatever's left once protein and fat are set: (total calories − protein × 4 − fat × 9) ÷ 4. That's deliberate — carbs flex with your goal instead of being fixed.

In short

BMR → × activity + sessions = TDEE → ± goal offset → floors → split into protein / fat / carbs. Five steps, two usable numbers, zero magic. If you'd rather not reach for a calculator, the app does it for you and re-adjusts calories every week based on your real weight trend.

Logical next step: once your macros are set, you need workouts to match. Read our guide to training at home with no equipment, and if you already play a club sport, see how to tailor your strength work to your sport.

This article is informational and not a substitute for medical advice. In case of a health condition, pregnancy or doubt, consult a healthcare professional.

Want to skip the maths? Join the Kaizmax waitlist: answer a short questionnaire and your tailored diet + training plan is ready in 2 minutes.