Peninsula Real Estate Guide
Why MLS and Assessor Square Footage Often Don’t Match, and Why It Matters
A discrepancy that shows up in up to 30% of listings, and the real consequences when it surfaces mid-escrow
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10% to 30% Of Listings With a Material Discrepancy |
~15% Of Contracts Affected by Appraisal Issues |
$200 to $1,500 MLS Fine for Misrepresentation |
ANSI Z765 The Appraisal Measurement Standard |
Pull up a listing on Redfin or Zillow, then check the county assessor’s own record for that same address, and the square footage often won’t match. This isn’t unusual, and it isn’t necessarily anyone lying. But it’s worth understanding before it surfaces as a genuine problem during your own transaction.
Why the Numbers Genuinely Differ
The MLS figure is typically entered by the listing agent, who technically has flexibility to use any reasonable source as long as it’s cited. County assessor records are based on building permit filings, not an actual field measurement, and they’re frequently outdated, especially for older Peninsula homes where a past addition wasn’t fully permitted or finalized. Appraisers use a specific national standard, ANSI Z765, which measures above-grade, finished, heated area from the exterior, a genuinely different methodology than either the MLS entry or the assessor’s permit-based number.
The Most Common Causes
| An addition was built without a finalized permit, so the assessor’s records never updated to reflect it |
| A finished basement or garage conversion is included in the MLS listing but excluded from the appraiser’s above-grade measurement |
| The assessor measured interior wall-to-wall space while the appraiser measured exterior dimensions, a genuine methodology difference |
| Older homes simply have less accurate, less frequently updated assessor records than recently built ones |
A Real Connection to Unpermitted Work
If a home’s actual square footage genuinely exceeds its assessor record, that’s often a sign of an unpermitted addition. For an FHA or VA loan specifically, that unpermitted space may need to be formally permitted before the transaction can close, which can meaningfully delay escrow if it’s discovered late.
What Actually Happens When the Appraisal Comes in Different
If you offer based on an MLS figure of, say, 2,200 square feet and the appraisal comes back measuring 1,950, several real consequences can follow: price adjustment pressure if the discrepancy is significant, a genuine appraisal gap requiring additional cash if the lower square footage drags the appraised value below your offer price, or a delayed closing while everyone works through the disagreement. Nationally, roughly 15% of real estate contracts encounter friction tied to appraisal issues, and square footage discrepancies are a meaningful share of that.
What Buyers Should Actually Do
| Compare the MLS figure against the county assessor’s own online property record before you tour seriously |
| Ask your agent directly what source the listed square footage came from, and whether any additions were fully permitted |
| If the discrepancy is large, budget for the possibility of an appraisal gap before you waive that contingency |
| Remember that a larger square footage figure isn’t automatically correct just because it’s what’s advertised |
What Sellers Should Actually Do
Best practice, according to real estate industry legal guidance, is to disclose any known square footage discrepancy to buyers rather than simply listing the more favorable number. If you’re unsure which figure is accurate, listing the more conservative one, with a note explaining any additional estimated space, protects you from misrepresentation exposure and potential MLS fines later.
Key Takeaway
A square footage mismatch between MLS, assessor records, and an appraisal is genuinely common, not automatically a red flag, but it’s worth checking early rather than discovering it during a tense moment in escrow.
Frequently Asked Questions
How common is a square footage discrepancy?
Independent analyses have found material discrepancies in roughly 10% to 30% of residential listings compared to appraisal measurements.
Does a smaller appraised square footage always lower a home’s value?
Often, though the actual impact depends on how significant the gap is and how the lender’s underwriting treats it.
Can unpermitted square footage stop my loan from closing?
It can, particularly for FHA or VA financing, which may require the space to be properly permitted first.
Where can I check a home’s assessor-recorded square footage myself?
Directly through the county assessor’s online property records, which are typically free and public.
| Related Reading | |
| What to Expect During the Home Appraisal Process | Understand how appraisers actually measure a home. |
| Seller Disclosures Explained: The TDS, SPQ, and What California Law Requires | Understand your broader disclosure obligations as a seller. |
| San Carlos Remodel and Addition Permits | Understand the permitting process that keeps assessor records accurate. |
| Home Inspection Contingency Waivers: How Risky Are They Really | Factor square footage verification into your overall risk assessment. |
Noticed a Square Footage Discrepancy on a Home You Love?
I can help you understand exactly what it means before you write an offer.
Holly Noto | Coldwell Banker Realty | DRE#01244498, DRE#01908304
580 El Camino Real, San Carlos, CA 94070
650.544.6185 | [email protected]
This content reflects general 2026 real estate industry reporting on square footage measurement standards and practices. This content is not legal or appraisal advice; consult a licensed appraiser for a definitive measurement of any specific property.
