Calorie and macro calculator
Updated: July 15, 2026
How many calories should you eat per day, and how do you split them across protein, carbs and fat? This calculator gives you both numbers in 10 seconds, using the Mifflin-St Jeor formula — the clinical reference. It's the same engine that runs inside the Kaizmax app. Free, no sign-up.
Estimate your needs in 10 seconds
The same engine as in the app — the clinical Mifflin-St Jeor formula, tuned to your goal.
How this calculator works
No magic: five steps, the same method that's coded into the app.
1. Your basal metabolic rate (BMR)
This is the energy your body burns at complete rest, just to keep you alive. The Mifflin-St Jeor formula estimates it from your weight, height, age and sex:
- Male: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Female: 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
2. Your total expenditure (TDEE)
We multiply your BMR by an activity factor reflecting your daily life outside training (from 1.2 if you're sedentary to 1.65 if your job is physical). Then we add your workouts on top, spread across the week — instead of drowning everything in a single factor. It's more accurate: training 4 times or 0 times actually changes your total.
3. The goal adjustment
- Lose fat: −20% of your TDEE. Enough to move every week, without the aggressive deficit that wrecks your energy and muscle.
- Build muscle: +10%. A light surplus: build without piling on fat.
- Maintain: at your TDEE, no offset.
4. Safety floors
Whatever the maths says, we never go below 1,500 kcal for men and 1,200 kcal for women. Below that, covering your micronutrient needs becomes nearly impossible.
Under 18, those two numbers stop meaning anything: a growing teenager often burns more than that at rest. The floor then becomes their basal metabolic rate plus 40%, never above their actual expenditure — protecting against undereating, yes; turning a weight-loss goal into a surplus, no.
And a weight-loss goal requested while underweight becomes maintenance (body mass index below 18.5). We won't refuse to answer you; we simply won't help you lose more.
5. The macro split
Protein is protected first, then fat, and carbs fill the rest:
- Protein: 2.0 g/kg when losing fat (to preserve muscle), 1.8 g/kg otherwise. 4 kcal/g. Not on the number the scale shows: the basis is the weight matching a body mass index of 25, capped by your actual weight. 2 g/kg is defensible around a normal BMI and absurd beyond it — fat tissue has no protein requirement. And whatever happens, protein never exceeds 35% of the day's calories.
- Fat: the greater of 28% of calories or 0.6 g/kg — essential for hormones. 9 kcal/g.
- Carbs: everything left. This is your training fuel. 4 kcal/g.
How to read your result
The big number is your daily calorie target. Below it, the split in grams of protein, carbs and fat. Aim for these on average across the week, not to the gram every day: one restaurant meal breaks nothing if the rest holds.
And above all: these numbers are a starting point, not gospel. Apply them for 2 to 3 weeks, watch what your weight trend does, and adjust. That's exactly what Kaizmax does for you automatically, every week.
Frequently asked questions
Are these numbers accurate?
The Mifflin-St Jeor formula is the modern reference for estimating energy expenditure, and it's the one dietitians use. It's still an estimate: real expenditure varies by around 10% from person to person. The right move is to start from this number, apply it for 2 to 3 weeks, then adjust based on what your weight actually does.
How often should you recalculate your calories?
Recalculate every 3 to 4 kg of weight change, or once a month. Your metabolism drops as you lose weight, so keeping your starting calories eventually stalls fat loss. The Kaizmax app does this for you every week, based on your real weight trend.
Why aim for around 2 g of protein per kilo?
In a calorie deficit, protein protects your muscle mass — without enough, you lose muscle along with fat. It's also the most filling macro, which makes the diet easier to hold. Beyond roughly 2.2 g/kg, research shows no further benefit.
Does this work for building muscle?
Yes. Pick the "build muscle" goal and the calculator applies a light surplus of about 10% above your expenditure. A light surplus is enough to build muscle without piling on unnecessary fat — you don't need an extra 1,000 kcal.
Does this replace a dietitian?
No. It's an indicative estimate, not medical advice. If you have a health condition, are pregnant, have a history of disordered eating, or are unsure, talk to a healthcare professional.
What's next?
Knowing your numbers is step 1. Step 2 is knowing what to eat and how to train to hit them. Download Kaizmax: answer a short questionnaire and your tailored diet + training plan is ready in 2 minutes — meals built to your macros, workouts matched to your equipment, and an engine that re-adjusts your calories every week as you progress.
Dig deeper: the full macro calculation method, how to hold a calorie deficit, and losing fat without losing muscle.
This article is informational and not a substitute for medical advice. In case of a health condition, pregnancy or doubt, consult a healthcare professional.