Bidder's contingency is internal to the contractor's bid — a percentage of direct cost held in reserve for items the bidder couldn't fully scope. Owner's contingency is held by the owner and used for owner-directed changes; it's separate from the contractor's contingency.
Higher contingency on: design-build projects (scope is still being defined), historic renovation (concealed conditions), public bids with strict change-order processes, projects with new or unfamiliar building systems.
Lower contingency on: repeat work for a known client, simple straightforward scope, tight market conditions where every percentage point matters. 3% is the floor for any commercial bid; 8-10% is common on complex work; 15%+ on truly high-uncertainty projects.