Two different numbers with two different jobs
Market value is what a willing buyer would pay a willing seller for your property. Assessed value is the number your county uses to calculate your tax bill. They are related, but they are not the same number, and the gap between them is where most property tax appeals live.
Every state defines the relationship differently. If you own property in more than one state, the same building economics can produce very different tax bills purely because of how each state converts value into an assessment.
How the three states we serve handle it
Georgia assesses property at 40% of fair market value. If the county believes your building is worth $5,000,000, the assessed value on the roll is $2,000,000, and the millage rate applies to that. The important number to check on a Georgia notice is the fair market value the county started from, because that is the number you can appeal.
Florida starts from "just value," which the courts treat as roughly equivalent to market value, then applies any caps and exemptions to reach assessed value and finally taxable value. For non-homestead property, including most commercial property, annual increases in assessed value are capped at 10%, but that cap resets when the property sells. The just value is the number the property appraiser defends, and the number an appeal challenges.
California is the different one. Under Proposition 13, assessed value is generally your purchase price, adjusted upward by at most 2% a year. That factored base year value can sit far below market value for long-held property. But when market value falls below the factored base year value, Proposition 8 requires the county to enroll the lower number. That is why California commercial owners can have a live appeal question every year even under Prop 13. We cover that mechanism in detail in our Prop 8 explainer.
Where the gap comes from
Counties value thousands of parcels at once using mass appraisal models. A model applies one set of assumptions across an entire class of property. It does not walk your building, and it rarely accounts for vacancy, deferred maintenance, functional problems with the layout, or what rents in your submarket actually did last year.
For commercial property this matters more than for houses, because commercial value depends on income. Two identical-looking buildings can have very different values if one carries long-term leases signed at yesterday's rents and the other sits a third empty. A mass appraisal model usually cannot see that difference. The assessment it produces is a reasonable guess for the average building, applied to yours.
Why the difference matters for an appeal
An appeal is not an argument that your taxes are too high. It is an argument that the county's value is higher than the evidence supports. That distinction decides what evidence matters:
- The county's own record for your property, which sometimes carries factual errors in square footage, age, or use.
- What genuinely comparable properties are assessed at and have sold for.
- For income-producing property, what the building actually earns, because appraisers and appeal boards weigh the income approach heavily for leased commercial property.
If the county's value is already in line with the evidence, there is nothing to appeal. Part of doing this honestly is saying so when that is the case.
One caution that applies in all three of our states: an appeal opens the valuation question, and in some circumstances a review board can raise a value as well as lower it. Checking for that exposure before filing is part of the work.
What to do with this
Pull your most recent assessment notice and find the market value or just value the county assigned, not just the tax amount. Then ask whether that number matches what you know about the building's income, condition, and market. If you want us to run that check against the county's own records, start a free analysis. It costs nothing, and if your value is already fair, we will tell you that plainly.
For filing windows in your county, see the appeal deadlines reference.