Renovation contingency: set aside 10–20%

Every renovation budget needs a 10–20% buffer.

Open a wall in an older house and you find things nobody priced: rot, old wiring, a drain in the wrong place. Contingency is the money you set aside for exactly that. 10% for a newer home and cosmetic work, around 15% for a kitchen or bath, 20% or more for an older house. Keep it as its own line, use it only for surprises (upgrades are change orders), and track estimate vs. actual every week.