Tools
The maths Letz uses, in the open
These are the formulas the app applies to your plan, with the same ranges and the same studies. Nothing is sent to a server: the maths runs in your browser.
Protein calculator
How much protein per day to support resistance training.
Split across 4 meals: 30–45 g
Range derived from the protein rules in the registry.
Energy expenditure
Basal metabolic rate by Mifflin-St Jeor and estimated total expenditure.
The Mifflin-St Jeor equation, the same one the app uses before it has enough data.
Calorie deficit
The deficit range that preserves lean mass, and the one that doesn't.
Above 1% of body weight per week, loss of lean mass increases consistently.
Range derived from the weight-loss rate rule.
Population estimates. Real expenditure varies between people and shifts over time; use this as a starting point, not as truth.
Registry rules cited here
- Protein and Training AdaptationSufficient protein can support gains in lean mass and strength alongside training; the response varies and does not increase indefinitely with higher intakes.
- Higher Protein Intake During a Calorie DeficitIn a deficit, higher protein protects lean mass and can even allow muscle gain alongside intense training; the effective range rises to approximately 1.6 to 2.4 g/kg.
- Estimating energy expenditureThe Mifflin-St Jeor equation is the most accurate formula for estimating resting energy expenditure, but it still errs in a significant portion of individuals.
- Rate of weight lossLosing weight slowly, at around 0.5 to 1% of body weight per week, better preserves lean mass, strength, and metabolic rate compared to rapid weight loss.
- Distribute protein throughout the dayDividing protein into servings of around 0.4 g/kg across four or more meals stimulates protein synthesis more than concentrating everything into one or two.