A calorie surplus means estimated energy intake is higher than estimated expenditure over a period, with actual change varying between people. This page provides a definition and practical context; it is not an individualized medical or nutrition prescription. Use the related tools and guides for calculations or programming decisions rather than treating a glossary definition as a result.
A conservative surplus for muscle gain typically sits in the 5 to 15% range above maintenance calories. Use the lean bulk calculator to set a surplus inside that band and to see an estimated weekly rate of gain scaled to your training age.
Sizing the surplus to your training age
How aggressive a surplus should be depends heavily on training age. Beginners and lifters returning from a long layoff can build muscle quickly enough to justify a slightly larger surplus (closer to 10 to 15% above maintenance) without a large fat-gain cost, because their muscle-building rate is naturally high. Advanced lifters, whose rate of muscle gain has slowed, see most of an oversized surplus stored as fat rather than converted to muscle, so a smaller surplus (5 to 10%) and a longer timeline produce a better ratio of muscle gained to fat gained.
A useful check: if the scale is climbing much faster than about 0.25 to 0.5% of bodyweight per week, the surplus is larger than needed for most trained lifters, and trimming it back preserves a leaner gaining phase without slowing muscle growth meaningfully.