I talk to sellers every week who have been watching their Zestimate the way some people watch the stock market. They check it regularly. They’ve seen it go up and down. They’ve built a number in their head around it. And by the time we sit down to talk about listing their home, that Zestimate has become the anchor for their entire financial plan.
I understand why. Zillow is everywhere. It’s the first place most people go when they start thinking about real estate, and the Zestimate is right there on the page — a specific number, presented with confidence, that feels authoritative. It looks like data. It looks like a valuation.
But here’s what I need every seller to understand before they make a major financial decision based on that number: the Zestimate is an algorithm. It is not an appraisal. It is not a comparative market analysis. It has never been inside your home. And in many cases — more than Zillow would like to admit — it’s wrong. Sometimes significantly.
Here’s what you need to know.
What the Zestimate Actually Is
The Zestimate is generated by a computer model that analyzes publicly available data — property tax records, recorded sales, public MLS data where available, and information that homeowners have submitted directly to Zillow about their own properties. The algorithm takes all of that data, runs it through a model, and produces a number.
What it cannot do is see inside your home. It doesn’t know that you renovated your kitchen three years ago or that your master bath still has the original fixtures from 1987. It doesn’t know that your home backs up to a green space that buyers love or that it’s under a flight path that affects desirability. It doesn’t know that your roof is brand new or that the HVAC is original to the house. It can’t feel the difference between a well-maintained home and a deferred-maintenance one.
It’s working with incomplete public data and producing a best guess. Zillow itself publishes accuracy statistics on the Zestimate, and even by their own numbers, the median error rate for off-market homes is several percentage points — which on a $400,000 home can represent a difference of $15,000 to $25,000 or more in either direction.
That’s not a rounding error. That’s a meaningful amount of money.
Why Zestimates Are Often Wrong
Beyond the fundamental limitation of not being able to see inside your home, there are several specific reasons why Zestimates frequently miss the mark.
They struggle in neighborhoods with limited sales data. When there aren’t enough recent comparable sales in your immediate area, the algorithm has to draw from a wider geographic range — which may include homes that aren’t truly comparable to yours. The less data available locally, the less reliable the estimate.
They lag behind fast-moving markets. Zillow’s model updates based on recorded sales, and recorded sales have a delay — there’s typically a gap of weeks between when a home goes under contract and when the sale is recorded publicly. In a market that’s moving quickly, that lag means the Zestimate may be reflecting conditions from two to three months ago rather than what’s happening right now.
They can be manipulated by user-submitted data. Homeowners can update certain facts about their own property on Zillow — square footage, bedroom and bathroom count, recent improvements. When that information is inaccurate, the Zestimate reflects the inaccuracy. And inaccurate square footage in particular can throw an estimate off significantly.
When Zillow Overestimates — and What It Costs You
An inflated Zestimate is probably the more dangerous of the two error directions for most sellers, because it feels good. When Zillow tells you your home is worth more than the market will actually support, it validates the number you wanted to believe. And that validation can lead directly to an overpriced listing.
I’ve covered the full cost of overpricing in another post on this blog, but the short version is this: an overpriced listing burns its best window of visibility at the wrong price, accumulates Days on Market, signals to buyers that something is wrong, and almost always ends up selling for less than a correctly priced home would have generated from the start.
Sellers who overprice based on a Zestimate don’t just miss out on their peak opportunity. They often end up accepting a final sale price that’s lower than what they would have received with accurate pricing from day one. The Zestimate that felt like good news at the beginning becomes a very expensive piece of misinformation by the time the transaction is over.
When Zillow Underestimates — and What That Costs You Too
A Zestimate that’s lower than your home’s actual market value is less common but equally problematic in its own way.
When sellers see a Zestimate that feels too low, one of two things tends to happen. Either they lose confidence in their home’s value and underprice their listing, leaving real money on the table. Or they distrust the first offer that comes in at or near fair market value — because it matches the Zestimate they’ve been conditioned to think is too low — and they hold out for a higher number that the market was never going to deliver.
Both outcomes cost money. And both stem from the same root problem: using an algorithm as a substitute for an actual market analysis.
A low Zestimate on a home with significant updates, superior condition, or features that the algorithm can’t detect is not a reflection of what the market will pay. It’s a reflection of what a computer model thinks based on incomplete information. The two things are not the same.
How to Increase Your Zestimate
Since Zillow is where most buyers start their search, your Zestimate does have some indirect influence on perception — not as a pricing tool, but as part of the overall impression buyers form before they ever contact an agent. Here are some practical steps to make sure your Zestimate is as accurate as possible before you list.
Claim your home on Zillow if you haven’t already. This gives you the ability to update your home’s facts directly. Check that your square footage is accurate — this is one of the most common sources of Zestimate error. Make sure your bedroom and bathroom count is correct. Update any recent improvements using Zillow’s home improvement tool — a renovated kitchen, a new roof, a finished basement.
Correcting factual errors in your home’s Zillow profile is worth doing. Just keep it in proper context: the goal is accuracy, not inflation. And no amount of Zillow profile optimization substitutes for knowing your actual market value from a real comparative market analysis.
What an Accurate Valuation Actually Looks Like
A comparative market analysis — a CMA — is what an actual home valuation looks like. It’s conducted by a local agent who knows your market, has access to complete and current MLS data, and can evaluate your home’s specific condition and features relative to what’s actually sold recently in your area.
A good CMA analyzes recent comparable sales — homes similar to yours in size, age, condition, and location that have sold within the last three to six months. It adjusts for differences between your home and those comparables. It looks at active competition — what else is on the market right now that buyers will compare your home to. And it considers current market conditions — whether inventory is rising or falling, whether homes are selling above or below asking, and how quickly homes in your price range are moving.
That’s a fundamentally different exercise than what Zillow’s algorithm does. It requires local knowledge, professional judgment, and eyes on the actual property. No algorithm can replicate it.
Get a Real Number Before You Make a Real Decision
The Zestimate is a useful tool for casual curiosity. It is not a tool for making one of the most significant financial decisions of your life. Before you set a list price, before you decide whether selling makes financial sense, before you build a plan around what you think your home is worth — get a real valuation from someone who actually knows your market.
If you own a home in Metro Atlanta and you’d like an honest, data-backed look at what your home is actually worth right now, that’s exactly what my free CMA Zoom call delivers. It’s 30 minutes, completely virtual, and there’s no obligation — we handle everything online so you don’t even have to leave your couch.
Ken Mandich is a Realtor® and Listing Expert with Complete Realty Team, serving Metro Atlanta with a focus on Cobb and Cherokee County. You can reach him at 404-410-6465 or [email protected].
