If the value of your home declines, shouldn’t your property tax bill decline as well?

Property taxes are based on the assessed value of the property, as determined by the local tax assessor. But assessments may not necessarily reflect the current market value of a property, according to Sam Heskel, executive vice president of HMS Associates, a Brooklyn appraisal firm. Instead, they are often a specific ratio of that value.

In addition, he said, tax assessments may not keep pace with changing markets. “Current assessments are probably based on property valuations that were made when prices were much higher,” he said.

If a home’s current assessment seems out of line, the homeowner should move quickly to appeal. “The main goal is to prove to the tax office that the assessment is wrong and that the fair market value of the property is significantly lower” than its value when it was assessed, he said.

Homeowners can file tax appeals on their own, or hire experts trained to determine the true current value of the property. “There are companies that offer services to help homeowners file tax appeals,” Mr. Heskel said.

Forms for filing an appeal are available at the local tax office. Municipalities have different deadlines for filing tax appeals, he said. In New York City, it is March 2.