Why are Zillow and Redfin home value estimates different?

Two computers, two opinions

The Zestimate and the Redfin Estimate are both automated valuation models. That is a fancy name for a computer program that estimates value from data, with no one visiting the house.

They are built by different companies, using different recipes:

• Zillow says its model uses county and tax records, MLS listing feeds and details owners provide, plus home size, location, room counts, nearby sales, prior sales and seasonal demand.
• Redfin says its model weighs more than 500 data points about the market, the neighborhood and the home. Because Redfin is a brokerage, it has said it has full MLS access, including details like a water location, a view or a busy street.

Different ingredients, different formulas, different results. It is two chefs making the same lasagna. You will recognize both, and neither will taste like your grandmother's.

They also refresh on their own schedules. Redfin has said its estimate updates daily for homes on the market and weekly for homes that are not. So on any given day, one site may have folded in last week's sale down the street and the other may not have yet.

Small data differences add up, too. If one site has your house as three bedrooms and the other has four, they are valuing two different houses. If your neighborhood has only a handful of sales a year, both models have less to work with, and their guesses can drift apart. A thin market is hard for a person to read. It is harder for a program that has never been inside.

How accurate are they, really?

Both companies publish a median error, the typical gap between the estimate and the eventual sale price. Here are the figures I could verify. Both companies update them, so check the current numbers before you quote one:

Median error means half of homes miss by less, and half miss by more. On a hypothetical $1,000,000 house that is not for sale, a 7% median error is $70,000. And half of homes miss by more than that.

These numbers also change over time. Redfin reported in 2019 that its off-market median error improved from 6.3% to 5.6%. Its 2026 figure is higher. Accuracy depends on the data, the market and the year.

Why listed homes are so much more accurate

The gap between about 2% and about 7% is the most useful thing in that table.

Once a home is listed, the models get fresh information: photos, a description, updated features and an asking price set by an agent who usually ran comps. Zillow says its estimate does not simply mirror the list price, but listing details can shift it. It also says a home that sits on the market a long time may switch back to an off-market estimate.

Put another way, the estimates get much smarter right after a professional looks at the house. That is a bit like grading a test after peeking at the answer key, then bragging about your score.

For your home, if it is not for sale, the 7% column is the one that applies to you.

What the models cannot see

A computer knows what the records say. It often does not know what is inside the walls.

• Condition. In my experience, buyers react to condition more than age. A model may treat a gutted-and-remodeled 1960s house like every other 1960s house on the block.
• Layout and quality. Two homes with the same square footage can live very differently.
• Unpermitted or detached space. Records may count a converted garage or miss a backyard cottage. A detached structure should be valued separately from the main house.
• Location details. Backing to a freeway, facing a park or sitting on a cul-de-sac can matter more than the zip code.

That is why both companies say it plainly. Zillow says the Zestimate is not an appraisal and cannot be used in place of one. Redfin says its estimate is not a formal appraisal or a substitute for an agent or appraiser.

What to do with two different numbers

1. Treat them as a range, not a verdict. If one says $900,000 and the other says $950,000, the truth may sit inside that range, or outside it.
2. Fix your home's facts. Both sites let owners update details. Wrong bedroom counts or square footage feed wrong estimates.
3. Check the sales yourself. Look at homes like yours that sold nearby in the last few months, and note how they compare in size and condition.
4. Watch the listed homes. The estimates on active listings are closer to the mark, and those listings are your competition.
5. Get an appraisal when money is on the line. For a sale, divorce, estate or refinance, a number has to hold up. At ValuedAudit, a desktop appraisal works without a site visit. You tell me what you know about the house and share photos if you have them. I bring the records, the market data and an evidence-based method that blends data science with human judgment, the way I have practiced it for almost two decades.

An estimate is a conversation starter. Your uncle quoting one at dinner is still not a comp.