Assessed Value vs. Market Value: What's the Difference for Property Tax?
Two numbers can describe the exact same house and be wildly different: what it would sell for today, and what the tax bill is actually based on.
The short answer
Market value is an estimate of what a property would sell for in a competitive sale under current conditions. Assessed value is a separate figure, calculated by a local assessor’s office, that’s used specifically to calculate the property tax bill — and it’s often a percentage of market value, updated on its own schedule rather than in real time. The two numbers are related but rarely identical, and the gap between them is normal rather than a sign of an error.
Why assessed value isn’t just market value
Assessors typically apply an assessment ratio, a percentage that converts an estimated market value into the assessed value actually used for tax purposes. In some places that ratio is close to full market value; in others it’s set much lower by policy. Either way, the assessed value is a derived figure, not a direct restatement of what a buyer would pay, which is why comparing the two numbers directly can be misleading without knowing the ratio behind them.
Reassessment cycles create lag
Market values can shift constantly as sales happen and conditions change, but assessed values generally only update on a fixed schedule — sometimes annually, sometimes only every few years, depending on the jurisdiction. Between reassessments, a property’s assessed value stays fixed even while its market value moves, which means:
- In a rising market, the assessed value often lags behind and understates current market value until the next reassessment catches up.
- In a falling market, the assessed value can end up higher than current market value for a while, which is often the trigger for an appeal.
Why the distinction matters for buyers and owners
Relying on assessed value as a stand-in for market value can be misleading in either direction — it might understate what a property could actually sell for, or it might overstate it, depending on when the last reassessment happened and how the local ratio is set. This is also a separate concept from an exemption that reduces taxable value for a primary residence, which changes the assessed figure for a different reason entirely. Anyone using assessed value as a rough substitute for market value in a bigger calculation — like estimating loan-to-value ratio before a refinance — is better served by a recent appraisal or comparable sales data than by the assessment alone.
Where the numbers come from
- Market value is generally derived from recent comparable sales, an appraisal, or broader market data.
- Assessed value is generally derived from the assessor’s valuation model, adjusted by the local assessment ratio, and updated on the jurisdiction’s own cycle.
- The tax bill is generally the assessed value multiplied by the local tax rate, meaning two identical houses in different tax districts can owe very different amounts even with similar assessed values.
This is also why a mortgage escrow account tied to property tax can see periodic adjustments even when nothing about the loan itself has changed — the assessed value and the tax rate behind it can shift on their own schedule.
The takeaway
Assessed value and market value answer two different questions — one is about what the tax authority will use to calculate a bill, the other is about what a buyer would likely pay — and treating them as interchangeable is where a lot of the confusion around property tax starts. Because assessment ratios, reassessment schedules, and tax rates are all set locally and can change, the specific relationship between the two numbers is worth checking directly with the local assessor rather than assumed.