What a clean surplus means

A clean surplus (or "lean bulk") is the strategy of eating slightly above TDEE to maximize muscle mass gain while minimizing fat accumulation.

Current science (Barakat et al., 2020) suggests a surplus of 200-500 kcal/day above TDEE for beginners and intermediates. Cyner uses a surplus of 10-15% of TDEE adjusted by training experience.

Muscle is built at a limited rate (0.5-1% of body weight per month in intermediates). Calories beyond the anabolic ceiling are deposited primarily as fat. There is no unlimited "eat to grow".

A "dirty bulk" (eating without control) may show more weight on the scale, but body composition studies show the muscle:fat ratio is worse. You'll need a longer, more aggressive deficit afterward.