How to Find Over-Assessed Commercial Properties: A Methodology Guide for Tax Appeal Firms

2025-07-14 · OverAssessed RE

How to Find Over-Assessed Commercial Properties: A Methodology Guide for Tax Appeal Firms

Identifying over-assessed commercial properties requires more than pulling an assessor roll and sorting by value. The core challenge is translating a county's certified assessed value — a number often set during a prior reassessment cycle — into a current, defensible market value that can be placed in front of an appeal board. That translation process involves three distinct data operations: CLR-adjusted market value derivation, automated valuation model cross-reference, and arm's-length comparable sale validation. Each step eliminates a category of properties that look attractive on the surface but will not survive board scrutiny.

This guide walks through that methodology in sequence. It is intended for tax appeal attorneys, property tax consultants, and multi-state firms that either conduct this analysis in-house or are evaluating a data vendor's methodology against their own practice standards.

Why the Assessor Roll Alone Is Insufficient

County assessor rolls are public record. In most jurisdictions, they contain parcel identification numbers, owner names, assessed values, property classifications, and acreage or square footage. In Pennsylvania, for example, the certified assessment data is maintained at the county level and updated annually, with the State Tax Equalization Board publishing Common Level Ratio (CLR) factors each year for each county.

The CLR factor is the ratio of assessed value to market value for arm's-length sales in a county during the prior calendar year. A CLR of 0.60 means that, on average, assessed values in that county are set at 60% of market value. If a commercial property's assessed-to-market ratio — derived by dividing its assessed value by its actual market value — is materially higher than the CLR, the property is over-assessed relative to the common level of assessment.

That analysis cannot be performed using the assessor roll alone. The assessor roll provides the numerator (assessed value). Deriving the denominator (current market value) requires additional data: sales comparables, income approach modeling, or an automated valuation cross-reference. Firms that skip this step and prospect based on assessed value alone are selecting on an incomplete signal.

Step 1: CLR Back-Derivation to Establish the Implied Market Value Threshold

The first operation is mechanical. For a given county and assessment year, divide the assessed value of each commercial parcel by the applicable CLR factor. The result is the implied market value at which that property would be assessed at the common level.

Example: - Property: office building, Bucks County, PA - Certified assessed value: $2,100,000 - 2025 CLR factor for Bucks County: 0.716 (published by STEB effective July 1, 2025, subject to verification against the current STEB release) - CLR-implied market value: $2,100,000 ÷ 0.716 = $2,932,960

If the actual market value of that property — determined through comparable sales or income approach — is materially below $2,932,960, the property is not over-assessed relative to the common level. If the actual market value is materially above $2,932,960, the property is over-assessed.

This threshold is the minimum bar. Properties that clear it move to the AVM cross-reference step. Properties that do not are removed from the working dataset regardless of how large their assessed value appears in absolute terms.

The CLR factor varies by county and by year. Pennsylvania's STEB publishes CLR factors annually, and applying the wrong year's ratio to a current appeal is a methodological error that will be identified by the assessment board. Any dataset that does not specify which CLR vintage was applied should be treated as unverifiable.

Step 2: Automated Valuation Model Cross-Reference

CLR back-derivation establishes a threshold. It does not establish actual market value — it establishes the market value implied by the current assessment at the common level. To determine whether the property is genuinely over-assessed, the actual market value must be estimated independently.

For commercial properties, the two primary approaches are the sales comparison approach and the income approach. Automated valuation models (AVMs) used for commercial real estate — sourced from platforms such as PropWire, CoStar, or county deed transfer databases — provide a preliminary market value estimate that can flag properties warranting deeper analysis. These models are not appraisal-grade; they are screening-grade. Their function is to separate the dataset into properties that warrant full comparable analysis from those that do not.

The AVM cross-reference produces a preliminary over-assessment gap for each flagged property:

Over-Assessment Gap = Assessed Value − (AVM Market Value × CLR Factor)

Properties where this gap is positive — meaning the assessed value exceeds what would be expected given the AVM market value and the CLR factor — move to the comparable validation step. Properties where the gap is negative or within a de minimis threshold (commonly 10–15% depending on the jurisdiction and asset class) are removed.

The threshold for flagging should be calibrated to the jurisdiction. In high-value commercial markets, a 15% over-assessment gap may represent a meaningful savings opportunity. In lower-value markets, a 15% gap on a $400,000 assessment may not justify the attorney's time at contingency. Firms should set their own minimum savings threshold — expressed in absolute dollar terms — and filter accordingly.

Step 3: Arm's-Length Comparable Sale Validation

The AVM cross-reference is a screening tool. It is not the evidence package. Before a property is presented to a client or placed in front of an appeal board, the over-assessment conclusion must be supported by arm's-length comparable sales — actual recorded deed transfers that reflect the market value of similar properties under conditions that an assessment board would recognize as valid.

This step is where most in-house prospecting efforts break down. Identifying comparable sales is straightforward. Verifying that those sales are arm's-length — and excluding the categories of transactions that assessment boards routinely disqualify — requires additional deed-level research.

Transactions to Exclude

Portfolio sales: A single deed transferring multiple properties as part of a portfolio transaction does not reflect an arm's-length indication of value for any individual parcel. The sale price reflects negotiation, bulk discount, and portfolio composition considerations that are distinct from individual parcel market value.

Related-party transactions: Sales between entities under common ownership or control — parent-subsidiary transfers, inter-family deeds, LLC-to-LLC transfers among related principals — are not arm's-length by definition. Many assessors will challenge comparables that include these transactions.

Foreclosure-related conveyances: Sheriff's sales, deed-in-lieu transfers, and REO dispositions are excluded from arm's-length analysis because they reflect distress conditions rather than a willing-buyer/willing-seller market.

Leasehold sales: A property sold subject to a below-market or above-market lease will have a transaction price that reflects the lease encumbrance, not the fee-simple market value. These require adjustment before use as comparables and in many cases should be excluded entirely.

Verification against county deed transfer records — not just the sale price data in an assessor roll or MLS extract — is the only reliable method for identifying and excluding these transaction types. The exclusion logic should mirror what the assessment board would apply, because that is the standard against which the evidence will be evaluated.

Step 4: Income Approach Cross-Validation for Income-Producing Properties

For commercial properties where rental income is the primary value driver — office, retail, industrial, multifamily above a certain unit count — the sales comparison approach alone may be insufficient. Assessment boards in major commercial markets will expect income approach support, particularly for properties where the income stream is demonstrably below market (a common driver of over-assessment for properties with long-term below-market leases).

The income approach requires:

  1. Market rent estimation: Derived from lease comps for similar space in the submarket. Sources include CoStar lease data, CBRE/JLL market reports, and county recorder filings for properties with publicly recorded leases.

  2. Vacancy and collection loss: Applied at the market vacancy rate for the property type and submarket, not the subject property's actual occupancy (unless vacancy is abnormally high and is itself a value-depressant being argued at appeal).

  3. Operating expense ratio: Applied at market norms for the asset class. Net operating income is the residual after market vacancy and expense loading.

  4. Capitalization rate: Sourced from recent comparable sales — the same transactions used in the sales comparison approach — to derive an implied cap rate. CBRE, Cushman & Wakefield, and CoStar publish quarterly cap rate surveys by market and asset class that provide corroborating support.

  5. Indicated value: NOI divided by the cap rate produces the income approach value indication. If the resulting value is materially below the CLR-implied market value from Step 1, the income approach provides independent confirmation of over-assessment.

Firms that skip the income approach for income-producing properties will be asked to provide it at the appeal board. Building it into the pre-screening methodology eliminates the back-fill research burden.

Step 5: Contingency Fee Projection and Case Prioritization

After the comparable validation step, the dataset contains a set of properties with a verified over-assessment gap, arm's-length comp support, and — for income-producing properties — income approach confirmation. The final step before presenting the dataset to a client or preparing appeal filings is to rank properties by expected contingency fee value.

This calculation is straightforward:

Projected Y1 Tax Savings = Over-Assessment Gap × Applicable Millage Rate

Projected Contingency Fee = Projected Y1 Tax Savings × Contingency Rate (typically 25–33%)

The millage rate is the sum of all applicable mills: county, municipality, and school district. In Pennsylvania, total millage varies significantly by municipality and school district. Applying a county-average millage to individual parcels introduces error; parcel-level millage from the county assessor or tax claim bureau is required for accurate projections.

Ranking by projected contingency fee allows a firm to sequence its outreach and intake by expected return on time invested. A property projecting $180,000 in Y1 savings at 30% contingency represents $54,000 in projected fees — a case worth a significant intake investment. A property projecting $8,000 in Y1 savings at 30% represents $2,400 in projected fees — potentially below the cost threshold for a formal appeal filing.

This prioritization step is often omitted in prospecting workflows that focus on identifying over-assessed properties without modeling the economics of pursuing them.

What a Complete Over-Assessment Dataset Looks Like

A dataset that has been processed through all five steps contains, at the parcel level:

This is the structure of the datasets OverAssessedRE delivers for any U.S. county within 48 hours of a discovery call. The Montgomery County, PA sample dataset — covering 1,605 commercial properties with $57.1M in total identified over-assessments — illustrates what this structure looks like applied to a complete county market.

Common Methodological Errors in Over-Assessment Prospecting

Applying a Prior Year's CLR Factor

CLR factors in Pennsylvania are published annually by STEB and become effective July 1. Applying a prior year's factor to a current-year appeal will produce an incorrect market value threshold. The error compounds if the CLR has moved significantly — which is common in markets where sales activity has shifted assessed-to-market ratios.

Using List Price Rather Than Sale Price as the Market Value Indicator

List price is not market value. Assessed value is compared against sale price — the arm's-length transfer price recorded in the deed. Datasets built on AVM estimates that are anchored to list price rather than recorded sale price will overstate or understate market value depending on market conditions.

Omitting School District Mills from the Savings Projection

In Pennsylvania, school district millage typically represents 60–70% of total property tax liability. A savings projection calculated on county and municipal mills alone — omitting school district mills — will understate the appeal value by a factor of two or more. Parcel-level millage should include all taxing authorities.

Treating AVM Output as Appeal Evidence

The AVM cross-reference in Step 2 is a screening tool. It is not admissible evidence at an appeal board hearing. Every property presented to a client or filed on appeal requires arm's-length comparable sales or an income approach analysis — or both. Firms that take AVM output directly to appeal without comp validation are presenting evidence that assessment boards have extensive experience challenging.

Applying This Methodology Across Multiple Counties and States

The methodology described here applies across jurisdictions with appropriate modifications for each state's assessment framework. Pennsylvania uses the CLR factor published by STEB. New Jersey uses the equalization ratio published by the Division of Taxation. Ohio counties use an assessed value that is set at 35% of fair market value by statute — which means the over-assessment analysis begins from a different baseline.

Each state's appeal process also imposes its own deadline structure, evidence requirements, and first-level versus formal appeal sequencing. The property tax appeal deadline calendar maintained by OverAssessedRE covers all 50 states and the District of Columbia, with jurisdiction-specific deadline dates and appeal level distinctions.

For firms operating in multiple states, building and maintaining a current understanding of each state's equalization methodology and appeal calendar is a material operational cost. On-demand datasets — ordered by county, delivered within 48 hours, with CLR or equalization ratio methodology applied correctly for the jurisdiction — eliminate the need to maintain that infrastructure internally.

Detailed methodology documentation for the OverAssessedRE data stack is available on the methodology page, including the specific logic applied for CLR back-derivation, AVM source selection, and arm's-length comp exclusion rules.

Getting a Custom Dataset for Your Target County

Tax appeal firms that want to apply this methodology without building the underlying data infrastructure can request a custom dataset for any U.S. county through OverAssessedRE. Each dataset is scoped to the requesting firm's target market, minimum savings threshold, and asset class focus — commercial, industrial, retail, office, or mixed-use. Comparable sales are arm's-length verified. Millage rates are applied at the parcel level. Appeal narratives are included for the top-identified properties.

Delivery is within 48 hours of a discovery call. Pricing is per-lead, with volume tiers available for firms ordering datasets across multiple counties. The 25% Replacement Guarantee applies to any property included in the dataset that does not qualify on appeal review.

To discuss a dataset for a specific county, book a 15-minute discovery call.

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