Renovation projects almost always cost more than the first quote suggests, which is why contractors and experienced homeowners build in a contingency buffer for unexpected surprises like hidden water damage or outdated wiring. This calculator estimates a realistic budget range using the square footage of the space and the finish quality you are aiming for, from basic touch-ups to premium materials and craftsmanship. Add your own contingency percentage on top, and you get both a target number and a safety margin to plan around before you start collecting contractor bids. It is a good starting point for setting expectations with a spouse, a lender, or a contractor before committing to a full renovation plan.