Weight Gain Calculator

Max Wishnofsky published the rule in the 1958 Postgraduate Medical Journal article 'Caloric equivalents of gained or lost weight'. He estimated that a pound of human adipose tissue stores about 3,500 kcal, based on adipose tissue being roughly 87 percent fat at 9 kcal per gram plus connective tissue and water. The rule is a useful back-of-envelope number for short-term planning, but Hall and colleagues (2011 Lancet) showed it overestimates long-term loss and gain because TDEE drifts as body composition changes. Treat the daily surplus this calculator returns as a starting estimate, then recheck your weight every 2 to 4 weeks and adjust.

Those ratios are calculator assumptions, not predictable biological outcomes. The share of weight gained as lean tissue varies with training status, resistance training, protein intake, genetics, sleep, and the size and duration of the surplus. A larger surplus can increase fat gain without guaranteeing faster muscle gain, but this tool cannot tell you whether your gain will be 50:50, 30:70, or another split. Track weight, waist, and performance over time and adjust gradually.

The 1.6 to 2.2 g/kg range is the consensus from the 2014 Helms, Aragon, and Fitschen review on natural bodybuilding contest preparation and the 2017 ISSN position stand on protein and exercise (Jager et al.). Both syntheses found that protein intakes above ~1.6 g/kg per day produced no additional muscle accretion in trained lifters, while intakes below it consistently underperformed for retaining and building lean mass. The 2.2 g/kg upper bound provides a safety margin for very lean or very athletic populations without proven added benefit beyond it.

A modest surplus is a practical starting range because it limits the rate of total weight gain while supporting training. It does not guarantee a particular muscle-gain rate or prevent fat gain, and 250 to 500 kcal is not a universal threshold. Start near the lower end, track your trend for several weeks, and adjust for training performance and unwanted waist gain.

Talk to a clinician or registered dietitian before starting a sustained calorie surplus if you are clinically underweight (BMI under 18.5), have a personal or family history of an eating disorder, are pregnant or breastfeeding, are under 18, take medication that affects appetite or metabolism (corticosteroids, antipsychotics, insulin), or have a diagnosed condition (hyperthyroidism, IBD, malabsorption, kidney disease). Recovery from clinical underweight in particular is a medically supervised process (NICE 2017, MARSIPAN), not a self-directed bulk. This calculator does not replace medical advice and cannot account for any of those situations.