How your plan is calculated

BioMech uses published equations for your calorie needs, fixed rules for your macros, and an optimiser for your portions. AI is used to choose foods and write the workout — never to calculate numbers. This page lists exactly what the system does.

1. Resting energy (RMR)

If you provide your body fat percentage, RMR is calculated from your fat-free mass: the Cunningham equation (500 + 22 × fat-free mass in kg) for bodybuilders, weightlifters and powerlifters, and a fat-free-mass and fat-mass based equation for recreational and endurance athletes. Without body fat, the Mifflin–St Jeor equation is used from weight, height, age and sex. Body fat can be estimated in the app with the U.S. Navy circumference method.

2. Daily energy (TDEE)

RMR is multiplied by an activity factor made of your daily activity outside the gym (sedentary 1.2, moderate 1.35, active 1.5) plus your training frequency (+0.1 for up to 3 days a week, +0.2 for 4–5, +0.3 for 6–7).

3. Calorie and protein targets by goal

Goal	Calories vs TDEE	Protein
Fat loss	15% deficit (20% if BMI > 30, 25% if BMI > 40); no deficit at BMI ≤ 18.5	2.2 g/kg
Bodybuilding cut	15% deficit (10% below 10% body fat, 5% below 8%)	2.4 g/kg
Muscle gain	5% surplus	2.0 g/kg
Bodybuilding bulk	10% surplus (5% from 20% body fat in men / 25% in women; maintenance from 25% / 30%)	1.75 g/kg
Recomposition	Maintenance	2.0 g/kg
Strength	5% surplus	1.8 g/kg
Endurance	Maintenance	1.8 g/kg
General fitness	Maintenance	1.6 g/kg

Fat is set at 0.7–0.9 g/kg depending on goal (never below 30 g), and carbohydrates fill the remaining calories. Above a BMI of 30, protein and fat are based on the weight at BMI 30 rather than total weight, because body fat carries little protein requirement. Calories never go below 1,500 kcal for men or 1,200 kcal for everyone else; if a target would, it is raised to that floor and you are told why.

4. Weekly adjustment

When you log weigh-ins, BioMech compares your average weight over the first and last week of the past six weeks. If you are cutting and your weight hasn't dropped over at least two weeks (with three or more weigh-ins), maintenance calories are lowered by 5%; if you are gaining and it hasn't risen, they are raised by 5%. Your plan tells you when this happens.

5. Building the meals

Foods come from a curated list with nutrition values from USDA FoodData Central, filtered for your diet type, exclusions and allergies. AI picks foods for each meal from that list only — it cannot use anything else. Every gram amount is then calculated by an optimiser that solves the whole day at once: your calorie, protein, carb and fat targets and each meal's share of them, within realistic portion sizes (no token 10 g servings, no 800 g of rice, eggs counted in whole eggs). If the chosen foods can't reach your targets, a suitable food is added and the day is solved again.

Members get three different rotating days, can swap any food (the day re-balances automatically), and see household measures alongside grams. All weights are cooked / prepared weight.

6. Accuracy checks

Every plan is checked against its targets and stores the result. A plan is considered on target when calories and protein are within ±5% and carbs and fat within ±10%. If a plan can't get there with realistic portions — usually a very high target in few meals — the dashboard shows the actual totals and suggests adding a meal, rather than presenting numbers that don't add up. In offline testing across thousands of simulated client profiles, over 90% of plans land within these tolerances.

7. Limits

Equations estimate averages; your real needs can differ, which is why the weekly adjustment exists. BioMech is not medical advice. If you are pregnant, have a medical condition, or have a history of disordered eating, speak to your doctor or a registered dietitian before changing your diet. The references behind these methods are listed on the About page.

Try the free diet plan generator →See sample meal plans