How we compute your calories

The computation chain

Every number ifit90 shows you — your calorie target, your protein grams, the narration text describing your plan — comes from one deterministic chain of calculations. Your answers (weight, height, age, sex, job type, step count, training days) go in one end; a full nutrition packet comes out the other. Nothing in between is guessed.

BMR: Mifflin-St Jeor

Basal metabolic rate — the calories your body burns at rest — is computed with the Mifflin-St Jeor equation, the most accurate published formula for both non-obese and obese adults, and the one we use as the base of every calculation:

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

This equation was derived on a US cohort. Indians tend to carry less fat-free mass at the same weight and height, so measured resting metabolic rate often runs 5-10% lower than the formula predicts. We treat the BMR output as a starting estimate, not a fixed truth — your actual weight trend over 2-3 weeks is what recalibrates it in practice.

TDEE: job-based activity

Total daily energy expenditure (TDEE) is BMR multiplied by an activity factor, plus your training. Instead of vague "sedentary / lightly active / very active" labels, we key the multiplier to Indian job types, because that maps much more directly to how people actually describe their day:

• Desk (IT, BPO, WFH, desk-bound roles) — factor 1.3
• Standing (teacher, shopkeeper, homemaker) — factor 1.45
• Field (delivery, sales rep, driver) — factor 1.6
• Physical (construction, farm work, loader) — factor 1.75

That base factor is then nudged by up to ±0.1 depending on your actual step count against a 6,000-step reference — someone in a desk job who walks 9,000 steps a day gets a small upward adjustment; someone in a field job who barely moves outside work gets a small downward one. Training is added on top as its own line item, at roughly 5 kcal per minute of resistance training, averaged across the week.

Target calories and the floor

Your target calories are TDEE adjusted by a deficit or surplus, sized to your goal:

• Fat loss: 20% deficit, capped at 750 kcal/day
• Muscle gain: 10% surplus, capped at 300 kcal/day
• Recomposition: a small 5% deficit, capped at 200 kcal/day
• General health: no deficit or surplus — TDEE itself

These caps exist because a bigger deficit is not a faster one in practice — published guidance (NHLBI) supports a 500-1,000 kcal/day deficit range, and larger cuts mostly cost muscle and adherence, not extra fat loss.

Whatever the deficit calculates to, it never pushes your target below a hard floor: 1,200 kcal/day for women, 1,500 kcal/day for men. This isn't an arbitrary cutoff — it's the threshold below which NHLBI guidance says a diet risks inadequate nutrition without medical supervision. If your calculated deficit would cross the floor, the floor wins and the deficit shrinks to fit above it.

Protein, fat, carbs

Macros are not split by percentages of calories, in that order. Protein is set first, in grams per kilogram of bodyweight, by goal:

• Fat loss: 2.0 g/kg
• Muscle gain: 1.8 g/kg
• Recomposition: 2.0 g/kg
• General health: 1.6 g/kg

(For higher-BMI users, protein is computed against a target bodyweight rather than actual weight, so the gram target stays realistic rather than inflated.) Fat is set next at a floor of 25% of total calories — never lower, because very-low-fat diets in a deficit tend to hurt hormonal health and make Indian home cooking impractical. Carbs get whatever calories are left over once protein and fat are accounted for, with a 50 g/day floor of their own so the plan never goes near zero-carb territory by accident.

The same computed packet also drives your daily water and step targets — 35 ml of water per kg of bodyweight (general published guidance runs 30-35 ml/kg), and a step target that starts from your current level and climbs by about 2,000 steps at a time toward a 7,000-10,000/day range. They're computed the same way as everything above: one formula, run once, referenced everywhere the number is shown.

Why this matters

Here is the actual promise behind ifit90's product: the AI-written narration that explains your plan never invents a number. Whatever the engine above computes — your BMR, your TDEE, your target calories, your protein/carb/fat grams — is the exact figure the narration text quotes back to you. The writing layer explains and contextualises; it does not calculate. If a number changes, it's because your inputs changed or the formula above ran again — never because the wording layer decided to round, estimate, or improvise. That separation between computation and narration is what makes every figure on ifit90 traceable back to a formula and a published source, not a guess.