MariposasCalorie Surplus
A calorie surplus happens when you consistently eat more calories than your body burns in a given day. Your body uses those extra calories as raw material, and when you're lifting or doing structured resistance training, much of that surplus goes toward building new muscle tissue. The number that determines your surplus is the gap between your total daily energy expenditure (all the calories you burn through basic body functions, digestion, and activity) and your total calorie intake. The nuance most people miss is that the size of the surplus matters a lot: a modest surplus of a few hundred calories per day tends to produce lean muscle gain with minimal fat accumulation, while a large, uncontrolled surplus leads to rapid fat gain alongside whatever muscle your body can actually synthesize. Muscle protein synthesis has a ceiling, so eating dramatically over maintenance doesn't build muscle faster, it mostly adds body fat. The phrase 'eating big to get big' is a real principle, but it works best when the surplus is deliberate and measured rather than just eating whatever fits.
Example
Say a 28-year-old who weighs 170 lbs burns roughly 2,600 calories on training days. If they eat 2,900 calories consistently, that 300-calorie daily surplus gives their muscles the energy and nutrients needed to repair and grow after workouts. Over several weeks, they'd likely see gradual strength and size gains without adding excessive body fat.