What If My House Facts Are Wrong or the Comps Are the Wrong Homes?

The complaints sound alike: the estimate says three bedrooms and the house has four, the square footage is a few hundred feet short, the map runs the lot line through the garage, the record still names the family you bought from, and the "similar homes" sit across the freeway. One mechanism sits behind all of them: an automated estimate reads a public file that nobody checked against your house, then builds a number on it. Here is where each error is born and how to fix the record and the comps yourself.

Where the facts about your house come from, and why nobody checked them

Every online estimate starts from the property card kept by the county assessor (in Texas, the appraisal district): living area, year built, bedrooms, bathrooms, lot size, last sale and a parcel sketch. The card exists for taxation. The Harris Central Appraisal District says so in its 2026 notice release: the district must value every property at 100 percent of market value as of January 1, and to meet the deadlines of the Texas Property Tax Code it uses mass appraisal across more than 1.9 million parcels¹. Nobody walks through 1.9 million houses. The card changes when a permit is posted, a deed is recorded or an owner protests, not when you finish the attic or when a clerk types 1,580 for 1,850.

Portal estimators, lead-generation calculators and agent valuation forms license or scrape those cards, merge them with listing feeds and recompute, so the error is used twice: to describe your house and to decide which sales count as similar. The guide to official home value data sources lists the public files behind a US valuation.

"It says 3 beds, it has 4": how room counts go wrong

A bedroom count on the card is a history of paperwork. The builder's plan said three; a later owner finished the room over the garage, added a closet and called it the fourth. Without a permit, or with a permit that closed before the characteristics file was updated, the county still has three, and many offices do not count rooms below grade at all.

The count matters beyond one line on a form, because models filter comparable sales by bedrooms: a four-bedroom described as a three-bedroom is matched with smaller, cheaper homes, and the undercount hits the value twice.

What to do: pull the card from the assessor's website and read every field. If a room is missing, gather the permit if one exists, a floor plan sketch and dated photos. In Texas the Comptroller's guidance is explicit: you may protest when "errors exist in the appraisal records regarding your property", on Form 50-132, and you may ask the appraisal district for an informal conference before any hearing². Other states run a characteristics correction at the assessor's office on the same evidence.

"The square footage is wrong": the county card versus an ANSI measurement

Square footage moves the number most, and it is the fact with two legitimate answers. Many assessors record the exterior footprint from plans or a sketch made from the street. An appraiser on a conforming mortgage works under Fannie Mae's Selling Guide, which requires the ANSI Z765-2021 measuring standard for finished and unfinished areas, above and below grade, of attached and detached single-family dwellings and manufactured homes, on every hybrid appraisal and every appraisal with an interior and exterior inspection³. Finished above-grade area, below-grade area and room count are reported as separate figures, so a finished basement is not folded into the living area³.

The scale is easy to underestimate. The 2023 American Housing Survey puts the median owner-occupied detached house at 1,900 sq ft and the median attached house at 1,600 sq ft⁴. A 200 sq ft error on a typical house is a tenth of the home, and the price-per-square-foot explainer shows why a crude model multiplies that tenth by the full average rate while a defensible adjustment uses the lower marginal rate.

What to do: measure the outside walls with a tape or a laser, sketch each floor and add up the finished above-grade areas. If the card is low, send the sketch and photos to the assessor. If it is high because it counts a garage or an unfinished space, your online estimate is inflated, and the buyer's appraiser will find out at the worst moment.

"The property lines are way off": parcel maps are not surveys

The line on the parcel viewer is a tax map, not your boundary. Sonoma County's Clerk-Recorder-Assessor says it directly: assessor maps are not surveys and should not be used in defining property lines; they are based on recorded documents and may not match what is measured on the ground or seen on aerial photographs, and a fence dispute with a neighbor is a private civil matter the assessor cannot resolve⁵. For an actual boundary the office points to a licensed land surveyor or civil engineer⁵. The drawing drifts because a parcel layer traced from paper maps was laid over aerial imagery with its own offset.

For the value, separate two questions. If only the drawing is off and the recorded lot size is right, nothing in the valuation changes. If the acreage on the card is wrong, correct the record with the recorded plat or deed. CheckValue shows the official aerial orthophoto of the plot, but the lot size you confirm drives the calculation, not the polygon.

"It still shows the previous owner": recording lag and the January 1 lien date

Ownership travels through layers that update at different speeds: the deed is recorded within days of closing, the assessor's ownership division processes it later, and the name on the assessment roll changes on the roll's own calendar. The Orange County Assessor states the California rule: by law the tax bill is issued to the owner as of the January 1 lien date, so a buyer who purchased on or after January 1 sees the prior owner's name until the following year, and a Preliminary Change of Ownership Report must accompany the recorded deed⁶. If that report was not filed at recording, the State Board of Equalization requires a Change in Ownership Statement within 90 days of the transfer, and fines owners who ignore the assessor's written request⁷. Data vendors pull the roll on their own schedule, so a website can lag the county by months. This is general information, not legal or tax advice.

For a US address, the CheckValue report names the owner of record from public county records, with owner type, last sale and mailing city. That data may not be used for credit, employment, insurance or tenant-screening decisions. The guide to finding out who owns a property covers the recorder and assessor routes if you need the current name today.

"It compared my house to a different neighborhood": what makes comps not comparable

An automated model picks comparables the cheap way: a radius around your address and a date window. Radii cross subdivision lines, school boundaries, a freeway and the edge of a flood zone without noticing. The professional standard is stricter. Fannie Mae's Selling Guide says comparable sales from within the same market area as the subject, including its subdivision or project, should be used when possible and must be used in certain instances; when an appraiser reaches into a competing neighborhood, the report must say so, address the differences and explain why those sales were chosen⁸. The Guide also wants at least three closed sales, preferably closed within the last 12 months⁸.

Five tests tell a comp from a stranger:

1. Same market area: the subdivision or the part of town a buyer of your house would actually shop in, not whatever lies within a mile.
2. Same type: a townhouse is not a comp for a detached house; a new build is not a comp for a 1970s ranch.
3. Similar size and rooms: living area within roughly 20 percent, same bedroom band, similar bathroom count.
4. Similar age and condition: a renovated house and an original one are different products on the same street.
5. Closed, arm's length, recent: a listing or a pending sale is supporting data, not evidence; a foreclosure or short sale belongs in the set only where such sales dominate the local market and the report says so; a transfer between relatives is not arm's length.

The method for finding and adjusting comps walks through the recorder, the assessor and the adjustment grid. If a valuation will not show you its sales, you cannot run these tests, which is the real complaint behind "the comps are not comparable".

Why free estimators get your house wrong, and why they are allowed to

The free number on a listing page is not sold to you; it is bait for an agent lead or an ad impression. That business model cannot afford a question per house, so it asks none: it reads the card, runs the model nightly and refreshes from the next feed, which may overwrite any correction you typed in. A point figure with no range looks authoritative, which is the point.

Regulators drew a line in 2024, but not around those sites. Six federal agencies (OCC, Federal Reserve, FDIC, NCUA, CFPB and FHFA) adopted the Quality Control Standards for Automated Valuation Models, in force since 1 October 2025. The rule obliges mortgage lenders and secondary market issuers that rely on an AVM to value a consumer's principal dwelling to run quality controls: confidence in the output, safeguards against tampering with the input data, no conflicts of interest, random sample testing of results, and compliance with fair lending law⁹. It reaches a lender's model, not the free estimate on a portal, which is why nobody audits it. The comparison of online home value estimators looks at what the portals publish about their own error, and the explainer on how an AI valuation works shows what a transparent model should print.

Worked example: a Houston four-bedroom recorded as a three-bedroom with 300 sq ft missing

The figures below are a hypothetical example at Harris County price levels, not a real transaction. For context, the appraisal district's May 2026 release puts 2025 Harris County sales prices at $426,558, up 2.5 percent from $422,590 in 2024, with inventory at 4.5 months in December 2025¹.

Subject: a 1998 two-story in a master-planned subdivision, 2,350 sq ft of finished above-grade area measured to ANSI³, four bedrooms, two and a half baths, a 7,400 sq ft lot. The card says 2,050 sq ft and three bedrooms, because the game room over the garage became a bedroom in 2016 under a permit that never reached the card.

Two wrong fields move the indicated value by roughly $46,000, about 12 percent, and the gap is not only arithmetic: the corrected filter finds a different set of houses, in the subject's own subdivision, as the Selling Guide asks⁸. The marginal $90 per sq ft (rather than the $180 average) is a judgment, as every size adjustment is, which is why the honest output is the range and not the point.

One caveat: the card cuts both ways. In Texas the appraisal district values at 100 percent of market value as of January 1¹, so correcting a low square footage can raise the appraised value and the tax bill. This is general information, not legal or tax advice.

What CheckValue does with your facts, and what it cannot do

The CheckValue flow is built around the complaint on this page. You type the address, and before anything is calculated you confirm the property type, living area, lot size, rooms, year built and condition, with the option to add your own photos. The free preview of your report shows the layout on screen before you pay. The calculated report lists the comparable sales it used with distance, closing date and the adjustment applied, prints each feature adjustment with its coefficient and source, and closes with a numbered reference list. Report prices are on the pricing page.

What it does not do matters just as much. Nobody measures your house, so if you confirm 2,350 sq ft the report values 2,350 sq ft; a buyer's appraiser will measure to ANSI and the lender will believe the appraiser³. The report does not change the county card or the owner of record; only you can file the correction. It is an AI valuation report with cited public sources, not a licensed appraisal, and where a lender or a court requires an appraiser's opinion it is preparation rather than a substitute.

This article is general information, not legal, tax or investment advice. Figures and rules carry the year they were published; check the cited source for the current version.

Josef Eckmair MBA

Co-founder, CheckValue · More than 20 years in real estate in Tenerife and Austria · Reviewed by Christian Eckmair

Josef Eckmair MBA is co-founder of CheckValue (CBDNOL GmbH, Ansfelden, Austria). He has more than 20 years of real estate experience in Tenerife and Austria and writes about appraisals, taxes, selling costs and valuations for professionals.

Articles by Josef Eckmair →

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