Zillow Admits Half Its Home Estimates Miss by 7% or More. On a Typical Chicago Home, That's About $30,000.
The number on your screen is a starting point, not a price. Here's how far off it can be, why Chicago is extra tricky for the algorithms, and a 10-minute way to find out what your home is really worth.
Be honest. You've checked your Zestimate this year. Maybe more than once. Maybe at 11 p.m. with a glass of wine, after your neighbor's place sold "for way more than we expected."
You're not alone. Almost every homeowner in Chicagoland peeks at that number. And here's the funny part: the companies that make those numbers are pretty upfront about how often they miss. Most people just never read the fine print.
So let's read it together, in plain English, with Chicago math.
What the websites say about their own accuracy
Zillow and Redfin both publish how accurate their home value estimates are. They report a "median error," which simply means: half of their estimates land closer than this number, and half land farther away.
The key thing to know is that they report two very different numbers. One for homes that are listed for sale right now, and one for homes that aren't for sale. If you're checking your own house before you list it, you're looking at the second one.
Estimate | Homes listed for sale | Homes NOT for sale (most of us) |
Zillow Zestimate | 1.9% median error | 7.0% median error |
Redfin Estimate | 1.88% median error | 7.32% median error |
Both companies update these figures from time to time, so you'll see slightly different numbers quoted around the web. The big picture doesn't change: once a house is listed, the estimate gets much better. Before it's listed, it's much looser.
Now let's put Chicago dollars on it
Over the three months ending August 2026, the median Chicago home sold for about $426,000, according to Redfin. In Cook County overall, the August median was about $383,716.
Home price | Zillow off-market error (7.0%) | Redfin off-market error (7.32%) |
$426,000 (Chicago median) | about $29,820 | about $31,180 |
$383,716 (Cook County median) | about $26,860 | about $28,090 |
Here's another way to picture it. If your off-market Zestimate says $426,000, the "typical" miss puts the real value somewhere between roughly $396,000 and $456,000. That's a window about $60,000 wide. And half the time, the real price lands outside that window.
The short version: An online estimate is a decent first guess about your neighborhood. It is a shaky guess about your specific house.
The catch in the "very accurate" number
That 1.9% figure for listed homes sounds impressive. But there's a reason it looks so good.
Zillow's methodology note says accuracy is measured by comparing the final sale price to the Zestimate shown on or just before the sale date. By that point, the home has been listed. The estimate has seen the asking price, the listing photos, the updated room counts, and how buyers are reacting.
Real-world example: a Sacramento appraiser named Ryan Lundquist once tracked a home listed at $380,000 with a Zestimate of $380,414. When the home went under contract for $335,000, the Zestimate quickly dropped to $346,364. Zillow has said its estimates update with new listing details, which is fair. It just means the "listed home" accuracy is partly borrowing from the work a human did to price the house.
That's not a scandal. It's just how the math works. But it's the reason the pre-listing number you see at 11 p.m. is the least reliable version of that estimate.
Why Chicago is extra hard for an algorithm
Algorithms are great at cookie-cutter homes: similar size, similar age, lots of recent sales nearby. Chicago is not a cookie-cutter city. A few things that trip them up here:
Mixed blocks. On one Chicago block you can have a condo, a brick two-flat, a gut-rehabbed single-family home, and a new-construction townhouse. Those are four completely different products sitting side by side, and a model can easily blend them together.
Two-flats and small apartment buildings. Redfin says its estimate only appears on single-family homes, townhouses, and condos. If you own a classic Chicago two-flat or three-flat, you may not get a Redfin Estimate at all.
Renovations that public records never saw. A finished basement, a new kitchen, a second bathroom, a new roof. If it isn't in the records the algorithm uses, the algorithm doesn't know it exists.
Condos are their own animal. Floor level, view, parking, the building's reserves, a pending special assessment, and whether lenders will finance units in that building can move a condo's price a lot. Most of that isn't in an online model.
A fast-moving market. Chicago's July median jumped 13.3% from a year earlier, per Illinois REALTORS. Models are built on sales that already happened, so in a quick market they can trail behind reality.
Three "Chicago home value" numbers. Same month. $92,000 apart.
This one surprises people. Here are three numbers for Chicago, all for June 2026:
Source | What it measures | June 2026 figure |
Zillow Home Value Index | Typical value of homes, built from Zestimates (sold or not) | $335,521 (up 3.9%) |
Zillow median sale price | Middle price of homes that actually sold | $381,667 |
Illinois REALTORS city median | Middle price of homes that closed through the MLS | $427,500 (up 6.9%) |
None of these is "wrong." They measure different things, over slightly different areas, in different ways. An index that includes every home, including ones nobody is selling, will usually look different from a median of the homes that actually sold that month.
The lesson is simple: a headline number about "Chicago" tells you very little about your house. Only sales of homes like yours, near yours, recently, can do that.
Why this matters: the estimate can move real money
You might think, "Who cares? It's just a number on a website." But buyers and sellers look at these numbers, and it shows up in prices.
A 2023 research paper titled "Does Machine Learning Amplify Pricing Errors in the Housing Market?" compared similar homes where the Zestimate was too high (by about 7%) against homes where it was too low (by about 7%). In the data they studied, the homes with the too-high estimate sold for about 2.2% more. On a $426,000 home, that's roughly $9,400, and it came from nothing but a number on a screen. The effect was bigger for smaller, more standard homes.
In other words, if your online estimate is lowballing your house, some buyers will walk in anchored to that low number. If it's too high, you might be tempted to overprice and sit on the market. Either way, knowing the real number protects you.
One more Chicago wrinkle: in May 2026, the local MLS (MRED) cut off its listing feed to Zillow during a legal fight, and roughly 43,000 Chicago-area listings were affected before a federal judge ordered the feed restored. It was a good reminder that what you see on any website depends on the data pipes behind it.
In fairness to the algorithms
To keep this balanced, online estimates do some things well:
They're free, instant, and good for spotting whether your area is trending up or down.
They're a reasonable place to start a conversation, especially in areas with lots of similar homes and lots of recent sales.
Human opinions can be off, too. Some agents quote a high number just to win a listing. That's why the answer isn't "trust a person instead of a computer." The answer is trust the evidence: real, recent, comparable sales, adjusted for your home's actual condition.
The 10-minute "what's my home really worth?" check
You can do most of this tonight, no agent required:
Look up your home on Zillow and Redfin. Write down both numbers. If they're far apart, that alone tells you the algorithms are unsure about your house.
Check the facts. Beds, baths, square footage, basement, garage, parking. If something's wrong, both sites let owners claim their home and correct the details. Redfin also lets you create an "Owner Estimate" where you pick your own comparable sales.
Look at the range, not the single number. Treat any estimate as "somewhere in this neighborhood," not "this exact price."
Find real sales of homes like yours. Same type (condo vs. single-family vs. two-flat), similar size, close by, sold in the last six months or so.
Be honest about condition. Is yours updated, original, or somewhere in between compared to those sales?
Get a free comparative market analysis (CMA). This is where a local agent pulls actual MLS sales, including details the algorithms never see, and gives you a realistic price range.
If you're thinking about selling
Buyers will see your estimate. If it's well below what your home is actually worth, your listing needs strong photos, a 3D tour, and clear details about upgrades to reset the conversation.
You may be able to turn the estimate off. Redfin says a listing agent can uncheck an "Allow Automated Valuations" option in the MLS, which prevents automated valuations from showing on third-party real estate sites for that listing. Worth discussing with your agent if your estimate is way off.
Price from the comps, not the Zestimate. In Cook County, over 43% of homes sold above asking in August, per Redfin. A realistic price can still attract strong offers. An estimate-driven price can go either way.
If you're buying
Don't build your offer around the Zestimate. Ask for recent comparable sales instead.
A big gap between the list price and the estimate is a question, not an answer. Sometimes the house is overpriced. Sometimes the estimate just missed a gut rehab.
Timing can help you. Realtor.com flagged late September into early October as one of the better weeks of the year to buy. We covered that here: Realtor.com says the best week of 2026 to buy starts Sunday.
Curious how much Chicago values have actually changed over the past few years? Read The Same Chicago House Is Worth 43% More Than It Was in 2021.
Want the real number? I'll run it for free.
I'm Jason Rosenberg, a Chicagoland Realtor® with 25 years in the business and over $100 million in sales, serving the city and the suburbs.
Send me your address and I'll put together a free, no-pressure home value review built on actual recent sales of homes like yours, not an algorithm's guess. No obligation to list.
And if you do decide to sell, you get full service at a lower cost:
1.25% listing commission. On a $426,000 Chicago home, that's about $5,325. At 2.5%, a rate some brokerages charge, it would be about $10,650. Commissions are always negotiable and vary by brokerage.
Zero Commission Clause. If you find your own buyer, you pay me no listing commission at all.
Cancel anytime. No long lock-in.
Full marketing. Professional photography, a 3D Matterport tour, and full online marketing.
Call or text: 312.882.9797
Sources
Redfin, "About the Redfin Estimate" (accuracy rates, property types covered, Owner Estimate, Allow Automated Valuations): redfin.com/redfin-estimate
Zillow, "How Accurate Is My Zestimate, and Can I Influence It?": zillow.com/learn/influencing-your-zestimate
Zillow, Chicago home values (Zillow Home Value Index, median sale price, data through June 30, 2026): zillow.com/home-values/chicago-il
Marc Lyman, "Zillow Zestimate and Why It Can't Be Trusted" (Zillow accuracy methodology note), May 2026: marclyman.com/zillow-zestimate
Inman, "What's the Deal With Zillow Changing Its Zestimates?" (Ryan Lundquist example), Aug. 2018: inman.com
"Does Machine Learning Amplify Pricing Errors in the Housing Market? The Economics of Machine Learning Feedback Loops," arXiv, 2023: arxiv.org/pdf/2302.09438
Redfin, Chicago housing market (3 months ending August 2026): redfin.com/city/29470/IL/Chicago/housing-market
Redfin, "Cook County, IL Housing Market Update: August 2026": redfin.com/blog
WTTW, "House Prices Jump in Illinois Amid Slow Pace of New Construction," Aug. 20, 2026 (Illinois REALTORS July data): news.wttw.com
Resideline, "Chicago, IL Housing Market 2026" (citing Illinois REALTORS June 2026 city median via Chicago Agent Magazine): resideline.com
HousingWire, "Judge orders MRED to restore Zillow listing feeds in Chicago," May 2026: housingwire.com
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