Why Zillow and Redfin Show Two Different Numbers for the Same Smithtown House
If you have ever typed your Smithtown address into two different websites and gotten two different answers, you are not doing anything wrong, the tools just work differently.
Homeowners check their value more often than they used to, and the easiest place to look is an online estimator. The trouble is that Zillow's Zestimate and Redfin's Estimate are both algorithms, not appraisals, and they are built from different ingredients. Knowing how each one is put together helps you read the number instead of just reacting to it.
Why the Two Numbers Do Not Match
Zillow describes its own tool plainly: the Zestimate is Zillow's estimate of market value, built from public, MLS and user submitted data, and the company says outright that it is not an appraisal. Redfin builds its estimate differently. Redfin is a licensed brokerage with direct MLS access, so its estimate leans on listing prices and recent closings as they happen rather than waiting for public records to catch up.
That difference in ingredients is the whole story. On homes that are actively listed, both sites tend to land close together because they are looking at the same detailed MLS information. On a home that is not for sale, both companies are guessing from public records and older sales, and that is where the two numbers start to drift apart.
The Gap Is Bigger Than People Think
Zillow publishes its own accuracy numbers, and they are worth sitting with. The company's published median error rate is about 1.9 percent for homes currently on the market, but jumps to roughly 7 percent for homes that are off market. A median error rate is not a worst case, it is the midpoint, so half of all estimates fall within that range and half are off by more.
Put that in real dollars. On a home valued around $800,000, which is close to where Smithtown's median sold price has been running this year, a 7 percent swing is about $56,000 in either direction. Redfin's own disclosed numbers are similar in shape, with a median error rate reported around 1.99 percent for active listings and nearly 7.9 percent for off market homes.
There is a second wrinkle that rarely gets mentioned. Neither Zillow nor Redfin can see inside your house, so renovations, a new roof, updated systems, or general condition do not factor into the number unless you manually tell the site about them. Two homes on the same block with the same square footage can carry the same online estimate even if one was fully updated last year and the other has not been touched since the 1990s.
What To Actually Do With the Number
Treat an online estimate as a starting point, not a verdict. If your home is not currently listed, you are looking at the wider, less reliable version of the tool, so give yourself room on either side of the figure you see. If you are getting ready to sell, the most useful check is not another algorithm, it is a look at what has actually closed near you recently, since that is the data a buyer's lender will lean on anyway.
If you want a second opinion on what your Smithtown home would likely bring in today's market, you can always check your number at /my-home-value/ or send me a question directly at /askmuds.