How much contingency should I budget for a renovation?

Plan 10–25% contingency on top of your contractor's quoted price, scaled by project complexity. Cosmetic refresh (paint, hardware, surface): 5–10%. Mid-tier remodel of an existing room without moving walls or plumbing: 10–15%. Full gut with new layout or older home (pre-1980): 20–25%. Pre-1940 homes routinely surprise on knob-and-tube wiring, lead pipes, lath-and-plaster substrate, and asbestos — budget 25–30% if you don't know what's behind the walls. The single biggest contingency-blowing item: discovering active termite or water damage during demo. Never start a renovation without 10% liquidity beyond your contract price.