Publishing advances are prepayments of future publishing earnings, not additional money. Publishers estimate your future publishing royalties and advance a portion, typically 60-80% of projected earnings over the deal term. You receive this upfront, then publishers recoup from your share of publishing royalties until repaid. After recoupment, you receive royalties according to your deal split. Remember, this only affects publishing income - your recording revenues and writer's share of PRS income remain unaffected.
Advances enable focusing on creativity without financial pressure. The amount of an advance depends on track record, catalogue value, and publisher confidence. Unrecouped advances typically aren't repayable, but may affect future negotiations. Some publishers offer rolling advances or minimum guarantees. Consider advance size against long-term earnings potential - sometimes smaller advances with better terms yield higher lifetime income.