Zillow’s automated valuation model pulls from publicly available data, sales records, tax assessments, square footage, and applies a broad algorithm to estimate value. The problem is that algorithm wasn’t built for a market like New Canaan. When you have Harvard Five mid-century moderns, historic colonials, and contemporary estates all within the same ZIP code, two homes with identical square footage can be worth $1 million or more apart. Zillow’s ZHVI for New Canaan currently sits around $1,684,777, well below the actual single-family median, which has been running between $2.5 and $3 million. A professional CMA accounts for what the algorithm can’t: architectural style, condition, proximity to the train station, school district access, and the specific buyer pool for your type of home. That’s the difference between a number built for the national market and one built for Fairfield County.