The estimated value of your home is a probability, not a price. When Zillow shows one number, Redfin shows another, and your lender's tool shows a third, none of them is "wrong" — they are three different automated valuation models (AVMs) reading three different slices of the same public record. This guide explains what actually goes into the number, why the confidence interval matters more than the point estimate, and how to correct the property record so future estimates track closer to reality. If you are still choosing which tool to use, start with our companion guide on what's my house worth. This piece assumes you already have an estimate in hand and want to understand it.
Key Takeaways
- AVMs blend recent comparable sales (roughly 60–75% of the weight), property features from the tax record, and market-trend adjustments — no AVM captures interior condition directly (Fannie Mae Collateral Underwriter fact sheet).
- The confidence interval — Zillow's "value range" or Redfin's "estimate range" — is a better signal than the point estimate. A $410,000 estimate with a $380,000–$450,000 range means the model itself only puts the true value inside that band with roughly 70–80% probability.
- Estimates from different sites disagree because each model weights comps, market trends, and record-card features differently. The National Association of Realtors documents typical AVM median error rates in the 2–4% range for on-market homes and 6–8% for off-market homes (NAR Field Guide to AVMs).
- You can improve your own estimate by correcting the record card at the county assessor's office — bedroom count, square footage, garage, finished basement — and, on Zillow, by claiming your home and submitting current photos.
- For a lending decision, a licensed appraisal is the default — with narrow exceptions. FHA appraisals follow HUD Handbook 4000.1; conventional appraisals are scored by Fannie Mae's Collateral Underwriter or Freddie Mac's equivalent against comparable-sales databases before the lender clears the file (Freddie Mac Selling Guide Ch. 5601). Eligible conventional files can qualify for an appraisal waiver via Fannie's Value Acceptance (formerly PIW) or Freddie's Automated Collateral Evaluation (ACE), decided by the AUS on a case-by-case basis.
What "estimated value" actually means
An estimated home value is one automated model's best guess at what your house would trade for today, expressed as a point estimate and — on the better tools — a probability range around that point. It is not an offer, not an appraisal, and not what the county thinks your house is worth for tax purposes. Those are four different numbers, built for four different purposes, and mixing them up is the fastest way to make a bad decision.
AVM vs CMA vs appraisal vs assessed value — the four numbers on your home
There are four estimates you'll bump into. An AVM (automated valuation model) is what Zillow, Redfin, and your lender's estimator produce — a model output built from public data. A CMA (comparative market analysis) is what a listing agent prepares by hand, blending comps with condition judgment. An appraisal is a USPAP-compliant valuation by a licensed appraiser, ordered for a loan. An assessed value is what your county uses to compute property tax — often set on a multi-year cycle and typically well below market. For a deeper walk through how these interact, see fair market value of a home.
Why an estimate is a probability distribution, not a single number
Every AVM is a statistical model. It doesn't know what your home is worth — it produces a distribution of plausible values and reports the midpoint. When Zillow prints "$412,000," that number is the mode of a curve; the real answer sits somewhere in a range around it. Treating that $412,000 as a fact is like treating a weather forecast's "63°F" as a guarantee — the model is expressing central tendency, not certainty.
Point estimate vs value range — read the range first
The single most useful habit when reading any home value estimate: look at the range before the number. A $410,000 estimate with a $395,000–$425,000 range is a confident model on a data-dense home. A $410,000 estimate with a $340,000–$500,000 range is a model that is essentially shrugging. Same headline number, wildly different signal.
How AVMs build the number (the four data inputs)
Every mainstream AVM is doing roughly the same job with roughly the same ingredients — the differences are in weighting and data recency. Understanding the inputs is what lets you predict where a given estimate is likely to be off.
Recent comparable sales — the half-mile / 90-day rule
Comparable sales carry the largest single weight in any AVM, typically 60–75% of the final estimate (Fannie Mae Collateral Underwriter fact sheet). Most models pull comps within roughly a half-mile radius and the last 90 days, then adjust for square footage, bed/bath count, and lot size differences. If your neighborhood turns over quickly and homes look alike, the AVM has plenty of signal and will produce a tight range. If you live on an atypical lot, in a historic district, or in a rural area where the nearest recent sale is two miles away, the comp pool thins out and the model widens the range to compensate. The specific mechanics of comp weighting are covered further in our overview of factors that influence home value.
Property features from the tax record
The AVM reads your public tax record for bedroom count, bathroom count, above-grade square footage, lot size, year built, and often garage type and basement status. That record is the foundation of the estimate. If your record card says three bedrooms and your house has four (a common issue after a permitted addition that never made it back into the assessor's file), every estimate on the internet is anchored to the wrong number.
Market-trend adjustments
The third input is a market-level correction — a ZIP-code appreciation rate applied to the raw comp average. If nearby homes closed 90 days ago and the market has moved 3% since, the AVM adds roughly 3%. This is why estimates rise (and fall) between weekly refreshes even when nothing about your house has changed.
What AVMs do NOT see
AVMs are blind to interior condition, finish quality, unpermitted renovations, unique layouts, views, corner-lot premiums, and school-boundary changes. They see a house on paper. Two homes with identical tax cards can trade $40,000 apart because one has been renovated and the other has 1998 laminate — and no AVM will catch that until an appraisal or a listing photo does.
Why Zestimate, Redfin Estimate, and Opendoor disagree
If you plug your address into four tools and get four different numbers, it is not because three of them are broken. Each model reads a different slice of the same data and weights it differently.
The methodology matrix
| Source | Primary data | Refresh cadence | Condition adjustment? | Output type |
|---|---|---|---|---|
| Zestimate | MLS + public records + user updates | Weekly | No (unless you claim + update) | Point estimate + value range |
| Redfin Estimate | MLS-first, public records | Weekly | No | Point estimate + range |
| Opendoor | AVM + video/photo condition review | Per request | Yes | Binding cash offer |
| Lender AVM (Chase, BofA, Pennymac) | Public records | Monthly / quarterly | No | Point estimate |
| Fannie Mae Collateral Underwriter | MLS + appraisal database | Per loan | Via appraiser | Risk score for the lender |
Zillow's model
Zillow's Zestimate covers more than 100 million homes and blends MLS feeds, public records, and user-submitted updates. It refreshes weekly and, per Zillow's own transparency page, quotes a median error rate near 2% for on-market homes and higher for off-market ones. It generally publishes the widest data footprint, which is why it is often the first number people see.
Redfin's model
Redfin's estimate leans on MLS data first, tightens the comp radius, and refreshes weekly. In dense metros with clean MLS coverage, Redfin's ranges tend to run narrower than Zillow's — but Redfin explicitly notes lower accuracy where MLS coverage is thin.
Opendoor's approach
Opendoor is a different animal. It is not a public AVM you scroll past on a Google result — it is a request that combines an AVM with a condition assessment (photos or a short video walkthrough) and produces a binding cash offer. That is why "the Opendoor number" often reads differently from a Zestimate: it accounts for interior condition and it commits to buying at the number, subject to a final on-site check.
Lender AVMs
Chase, Bank of America, Pennymac, and others publish AVM widgets that pull public-records data (no MLS) and refresh monthly or quarterly. They are tuned for lead generation — often optimistic on the point estimate — and rarely publish a confidence interval. Bankrate's overview of online home value estimator tools documents the refresh-cadence differences across the major lender AVMs.
The confidence interval — the number that actually matters
Every serious AVM publishes a range around its point estimate, and that range is the single most useful piece of information the tool gives you. It is not marketing. It is the model telling you how much data it had to work with.
What the range means
The range is a modeled probability band. When Zillow prints "$381,000 – $443,000," it is saying the model puts the true market value inside that band with roughly 70–80% probability. There is a 20–30% chance the real number sits outside the range entirely. Once you read it that way, "my Zestimate is $412K" stops sounding like a fact and starts sounding like the middle of a bell curve.
How wide is "too wide"
A useful heuristic: divide the width of the range by the point estimate. Under 10% is a confident model. 10–15% is normal. Over 15% is a model warning you it doesn't have enough data. A $410,000 estimate with a $340,000–$500,000 range (a 39% span) is telling you that the AVM found thin comps and could not resolve the price closer than a $160,000 window. That is not an estimate you can plan against — that is a signal you need a CMA or an appraisal.
Why rural, historic, and unique homes get wider ranges
The IAAO Standard on Mass Appraisal — the industry rulebook for mass valuation — explicitly permits wider tolerance for atypical properties, because the underlying comp math simply produces less certainty. If you live on 5 acres in a semi-rural area where the nearest recent sale is a smaller ranch home 1.8 miles away, no AVM is going to give you a tight range. That is a feature of the model, not a bug.
How to update your record card so the estimate tracks reality
Because AVMs anchor to your public tax record, correcting that record is the single highest-leverage move you can make to improve every estimate on the internet at once. This is boring, unglamorous work — but a corrected record card can move an estimate 3–8% overnight.
The county assessor record
Start at your county assessor's office. Every state provides an online lookup where you can view the record card your assessor has on file: bedroom count, bathroom count, above-grade square footage, lot size, year built, garage, basement finish, deck. Read it line by line and note any errors. Common problems: a permitted bedroom addition that never made it into the file, a finished basement listed as unfinished, an old 1.5-bath count on a house that now has 2.5. The correction process varies by county but usually involves submitting a form plus documentation (permits, floor plans, or an inspector's letter) and, in some cases, allowing an assessor visit.
Zillow claim + owner updates
Claim your home on Zillow and submit current photos, current bedroom/bathroom counts, and a list of recent renovations. Zillow will not blindly accept your numbers, but owner-submitted data enters the Zestimate model as a weighted input and typically tightens the value range within a refresh or two.
Redfin owner dashboard
Redfin offers a similar owner dashboard where you can update home facts and add photos. The impact is smaller than on Zillow (Redfin leans harder on MLS-only data), but it doesn't hurt.
Opendoor — correcting the details behind your preliminary offer
If you've requested an Opendoor offer and the preliminary number reads low, the fix is direct: contact Opendoor support at 888-352-7075 or support@opendoor.com and flag the specific details you believe are wrong (finished square footage, bedroom count, recent renovation, garage type). Opendoor recalculates the offer against the corrected details before final assessment. This is not a Zillow-style "we'll consider it" — it is a support ticket that gets the number rebuilt. For the underlying help center walkthrough of what Opendoor asks for and how the preliminary-to-final flow works, get a free home value estimate from Opendoor.
When the estimate is not enough (and what beats it)
An AVM is fine for a rough plan. It is not fine for a loan decision, a tax appeal, or a listing price. Here is what actually beats an estimate at each use case.
Lending decisions
Lenders will not close loans on a public AVM like a Zestimate. Conventional and FHA loans generally require a traditional appraisal — FHA under HUD Handbook 4000.1, conventional scored through Fannie Mae's Collateral Underwriter — ordered by the lender through an appraisal management company, costing $500–$700 in most metros and taking 5–10 business days. There is a narrower exception on the conventional side: eligible files can receive an appraisal waiver via Fannie Mae's Value Acceptance program (formerly PIW / property inspection waiver) or Freddie Mac's Automated Collateral Evaluation (ACE), where Desktop Underwriter or Loan Product Advisor accepts the value estimate without a full appraisal. Waivers are offered case by case (typically limited-cash-out refinances, some purchases, LTV caps apply) and rely on Fannie/Freddie's own model — not the borrower's Zestimate. Whether waiver-eligible or not, the AVM you look at online is still just a sanity check; the appraised value (or the waiver value) is what the loan file will use.
Property-tax appeals
For a property-tax appeal you need the assessor's own record card, three to five recent comparable sales that closed near assessment date (not today's date), and, in most jurisdictions, evidence of specific errors on the record card. A Zestimate carries no weight in an assessment appeal — assessors already know their data is different from Zillow's data and treat it as noise.
Pre-listing pricing
For pricing a home you plan to list, a CMA from an experienced local listing agent will typically beat an AVM by 2–4 percentage points. The reason is condition: the agent walks the house, calibrates the finish level against recent closings, and factors in the specific micro-market (school boundary lines, one-way streets, cul-de-sac vs through-street). No AVM does that. If you want to sanity-check your own thinking before an agent meeting, our guide to factors that influence home value walks through the specific inputs a good CMA weighs.
Certainty on sale price
A binding cash offer — Opendoor's product — removes the estimate-vs-appraisal-vs-buyer-financing risk stack entirely. You know the number before you commit and you close on your schedule. The trade-off is honest: if maximizing sale price is your top priority and you have 60+ days to list, show, negotiate, and endure an inspection contingency, a well-run listing with an experienced agent will usually net more. Opendoor is built for sellers who value certainty and speed over squeezing every dollar. Both paths are legitimate; the choice comes down to what you're optimizing for.
A worked example — reading three estimates on the same house
Consider a real profile: a 3-bed, 2-bath, 1,850-sqft home built in 1998 in a suburban Phoenix neighborhood with steady turnover.
The three numbers
- Zestimate: $412,000 (range $381,000–$443,000)
- Redfin Estimate: $398,500 (range $373,000–$424,000)
- Lender AVM (public-records only): $405,000 (no range)
What the disagreement is telling us
The point estimates differ by $13,500 — about 3.4% — which is inside the normal disagreement band for a data-dense metro. Zillow prints higher because it is picking up recent owner-submitted photos showing a partial kitchen update; Redfin's MLS-first model doesn't see that update because there's no permit or recent listing to hang it on. The lender AVM sits in the middle because it is drawing from public records only and doesn't weight either input.
More importantly, the ranges overlap. Zillow's $381K–$443K and Redfin's $373K–$424K share the band $381K–$424K. That is where the two models agree, and it is the strongest signal in the data.
What to do next
Take the midpoint of the two published ranges (~$405K), widen your working band to the union of the two ranges ($373K–$443K), and treat that as your pre-listing planning value. If you're about to talk to a listing agent, hand them that band and ask which end they think the market is at today. If you're about to request an Opendoor offer, that band is your reality check on what comes back. If you're refinancing, order the appraisal knowing that anything in the $373K–$443K band should not surprise you.
Disclosure
This article is provided for informational purposes and reflects home valuation practices as of 2026. AVM methodologies, refresh cadences, and reported accuracy figures change over time; consult the source you are using for its current published methodology. For lending, tax-appeal, or legal decisions, consult a licensed appraiser, tax professional, or attorney rather than relying on an automated estimate.
