Start with a plan you can observe
Body recomposition describes changing the balance of fat and lean tissue, often with the aim of losing fat while gaining muscle. A calculator cannot tell you how much of either will change. It can give you a consistent starting point for food and a checklist for reviewing your training and progress.
Choose estimated maintenance or a small deficit. Neither choice guarantees fat loss or muscle gain. Your actual energy needs, training history, consistency, and recovery all affect what happens next.
How we calculate the starting estimates
Resting energy: the Mifflin–St Jeor equation uses weight in kilograms, height in centimeters, age, and one of the original sex-specific coefficients. The coefficient is a limitation of the source equation, not a complete description of your physiology.
Resting kcal = 10 × kg + 6.25 × cm − 5 × age + coefficient
Coefficient: +5 for the male equation or −161 for the female equation.
Activity: we multiply the resting estimate by 1.2, 1.375, 1.55, or 1.725. These common activity multipliers are rough planning assumptions, not measurements and not part of the original Mifflin equation.
Planning approach: maintenance uses the activity-adjusted estimate. Small deficit uses 95% of that estimate. The 5% setting is Brolic’s modest planning scenario; it is not a scientifically established “recomp formula.”
Protein: the displayed range is 1.6–2.2 g per kilogram of entered body weight. Resistance-training research informs this range, but individual needs vary and more is not automatically better. The calculator does not estimate body fat, infer lean mass, or project a transformation date.
The tool is bounded to adults aged 18–85, 40–250 kg, and 130–230 cm. Values outside those ranges are outside this tool’s scope. Low calorie estimates receive a screening message; the screen is not a personalized safety assessment.
An example you can check
For an 80 kg, 180 cm, 30-year-old using the male equation and moderate activity:
- Resting estimate: 1,780 kcal/day.
- Activity-adjusted maintenance: 1,780 × 1.55 = 2,759 kcal/day.
- Small-deficit scenario: 2,759 × 0.95 ≈ 2,621 kcal/day.
- Protein range: 80 × 1.6 to 80 × 2.2 = 128–176 g/day.
Keep four kinds of evidence together
- Food: record intake and protein consistently enough to compare days.
- Training: record exercise, load, reps, and effort. Keep comparisons specific to the exercise.
- Weight: compare weekly averages from similar weigh-in conditions.
- Measurements and photos: use consistent conditions and allow time between comparisons.
A single weigh-in or photo cannot identify a change in muscle or fat. Use several weeks of observations, and seek individualized help when the general planning assumptions do not fit your situation.
Common questions
Why don’t you ask for body-fat percentage?
Home estimates can add uncertainty. This version uses a transparent bodyweight-based calculation and does not pretend to know your lean mass.
Should I eat back exercise calories?
The activity setting already includes training. Adding a second exercise estimate would count the same activity twice.
Does this tell me whether I should cut, bulk, or recomp?
No. It compares two starting scenarios. It does not assess your health, prescribe a diet, or determine the best goal for you.
Sources & method
Written by the Brolic team. These references explain the evidence and assumptions; this page does not replace individualized professional advice.
- Mifflin et al. — Predictive equation for resting energy expenditure (1990) — The resting-energy equation used here.
- Morton et al. — Protein and resistance-training adaptations (2018) — Research informing the protein planning range; not a guarantee of recomposition.