Assessment

Quick Definition

A property assessment is the official valuation of real estate assigned by a local government assessor for property tax purposes. The assessed value is multiplied by the local tax rate (mill rate) to calculate the annual property tax bill. Assessed values often differ from market value, either intentionally (through an assessment ratio less than 100%) or due to infrequent reassessment cycles that cause values to lag the market.

What It Means

The assessment process is how local governments establish the tax base for funding schools, infrastructure, and public services. Unlike a market appraisal (which estimates what a buyer and seller would agree to), an assessment is a governmental determination made for taxation purposes. It may or may not closely track market value, depending on the state's laws and how recently properties were reassessed.

Assessment vs. Appraisal vs. Market Value

How Assessed Value Is Determined

County assessors typically use mass appraisal software (CAMA, or Computer Assisted Mass Appraisal) to value all properties simultaneously using statistical regression models. Individual property nuances are often missed, which is why appeals are sometimes successful.

Assessment Ratio: The Key Concept

Many jurisdictions do not assess property at 100% of market value. They apply an assessment ratio:

Assessed Value = Market Value x Assessment Ratio

Example: Illinois property

• Market value: $450,000
• Assessment ratio: 33.33%
• Assessed value: $150,000
• Mill rate: 90 mills (9%)
• Annual tax: $150,000 x 9% = $13,500 (effective rate on market value: 3%)

2026 Assessment Roll Trends

Assessment rolls across the US are showing continued growth in 2026, driven by property transfers, new construction, and inflation adjustments:

Sources: County assessor announcements (July 2026), CalTax, Mass.gov.

In California, Proposition 13 limits assessed value increases to 2% per year for existing owners. Growth in assessment rolls comes primarily from property transfers (which reset assessed value to purchase price), new construction, and the annual inflation adjustment. In Indiana, residential assessed values grew 7.3% statewide in 2026, while commercial properties rose 15% and industrial properties rose 25.8%.

Reassessment Cycles

Assessments are updated on different schedules by jurisdiction:

Lag risk: In rapidly appreciating markets, infrequent reassessment means assessed values significantly understate market value. This creates a "catch up" reassessment shock when the next reassessment occurs. Conversely, in declining markets, assessed values may exceed market value, and owners should appeal.

Special Assessments vs. Regular Assessments

A special assessment appears on a property's tax record as an additional charge, typically payable over 5-20 years. It attaches to the property and must be disclosed in a sale. Unpaid special assessments can become liens.

How to Review and Appeal Your Assessment

Step 1: Request the assessor's property record card. It shows square footage, bedroom/bath count, quality rating, and other factors the assessor used.

Step 2: Compare to recent comparable sales. Find 3-5 properties that sold in the last 12-24 months with similar features. Calculate the implied assessment ratio for each comp.

Step 3: Identify errors. Wrong square footage, wrong number of bedrooms, incorrect construction quality rating, recent damage not reflected.

Step 4: File an informal protest with the assessor's office. Submit comps and any error documentation.

Step 5: If unsuccessful, file a formal appeal with the Board of Review or Assessment Appeals Board.

Appeal deadlines are strict, typically 30-90 days from receipt of the assessment notice. For example, Riverside County, CA's 2026 appeal filing period runs from July 2 through November 30, 2026. Missing the deadline forfeits your right to appeal for that assessment year.

Assessment and Disclosure in Real Estate Transactions

In California, a home purchased for $800,000 that was previously assessed at $300,000 under Prop 13 will be reassessed to $800,000 upon sale. The new owner's property tax bill could jump from approximately $3,000/year to $8,000/year. This is one of the largest closing costs surprises for out-of-state buyers unfamiliar with Prop 13.

Key Points to Remember

• Assessment is the government's valuation for tax purposes. It may differ significantly from market value.
• Assessment ratio determines what percentage of market value is taxed, varying from 33% to 100% by state.
• Mass appraisal software often misses individual property nuances. Errors are appealable.
• Reassessment timing creates tax surprises: lag benefits long-term owners; catch-up shocks new ones.
• 2026 assessment rolls show 3-5% growth in California counties and nearly 10% in Indiana, driven by transfers, construction, and inflation adjustments.
• Special assessments for infrastructure improvements attach to the property and transfer to new buyers.
• Appeal deadlines are strictly enforced, typically 30-90 days from assessment notice.
• California Prop 13 caps annual increases at 2% but resets to purchase price on sale, creating major tax jumps for new buyers.

Common Mistakes to Avoid

• Not checking the assessor's property record card for errors: Assessors use mass appraisal models that can misstate square footage, bedroom count, or quality rating. A 200-square-foot overstatement on a $450,000 home in a 3% tax jurisdiction costs $270/year in excess taxes.
• Missing the appeal deadline: Most counties give you 30-90 days from the assessment notice to file. Riverside County's 2026 window is July 2 to November 30. Miss it and you are stuck with the assessment for the entire tax year.
• Assuming your assessed value equals market value: In states with assessment ratios below 100% (Illinois at 33%, Michigan at 50%), the assessed value is a fraction of market value. Do not use assessed value as a proxy for what your home is worth.
• Underestimating post-purchase property tax increases: In California and other states that reassess on sale, buying a home can trigger a massive property tax jump. Budget for the new tax amount, not the seller's current tax bill.
• Ignoring special assessments: A pending sewer or road improvement assessment can add hundreds or thousands to your annual tax bill for years. Always check the title report for outstanding special assessments before closing.
• Failing to appeal when market values decline: If your home's market value has dropped below the assessed value, you are overpaying. File an appeal with recent comparable sales showing the decline.

Frequently Asked Questions

Q: Why is my assessed value different from what my home would sell for? A: Multiple reasons: your state may use an assessment ratio below 100%; the assessor's last mass appraisal may pre-date recent price changes; or the assessor's model may have missed improvements or unique features of your property. In most states, you can find the assessor's explanation of methodology on the county website or by calling the assessor's office.

Q: Can my property taxes go up even if I haven't made improvements? A: Yes. This happens through general reassessment (the county updates all values to reflect current market conditions) or through increased mill rates (taxing districts raise their rates to fund budgets). In states with assessment caps like California's Prop 13 (limits increases to 2%/year), taxes rise slowly. In states without caps, a full reassessment to current market value can significantly increase taxes even with no property changes.

Q: What is an "equalization factor" on my tax bill? A: Some states (notably Illinois) use an equalization factor (also called a multiplier) applied to assessed value to bring the assessment into alignment with state standards. If the state determines that a county is under-assessing at 25% of market value when the standard is 33%, it applies a multiplier to raise all assessments. The equalized assessed value (EAV), after the multiplier, is what the tax rate is applied to.

Q: How does California's Proposition 13 work in 2026? A: Prop 13 limits assessed value increases to 2% per year for existing owners. When a property is sold, the assessed value resets to the purchase price. In 2026-27, California assessment rolls are growing 3-5% on average, driven by the 2% inflation adjustment plus property transfers and new construction. A home bought for $500,000 in 2010 that is now worth $1.2 million may still be assessed at only $600,000, creating a significant tax gap that resets on sale.

Q: How do I find my property's assessed value? A: Visit your county assessor's website and search by address or parcel number. Most counties provide the assessed value, tax bill history, and property characteristics online for free. You can also request a copy of your property record card by calling or visiting the assessor's office.