That, of course, is a tricky business. Just think of how often you've rolled your eyes at the price a neighbor is asking for her house.
But if you think your assessment is wrong, you should file a first-level review, which must be done by March 31. The appeal paperwork arrived with the new assessments.
On the form, you must check off a box or boxes indicating why you are appealing. There are three choices:
Market Value, meaning you believe the property was assessed at more or less than its actual market value.
Nonuniformity, if you think the city has valued your home, land, or commercial building differently from other properties.
Incorrect exemption or abatement, if you think the city has incorrect information about your property-tax abatement. This section does not have anything to do with the proposed homestead exemption, which would allow homeowners to reduce the value of properties by an amount determined by City Council.
The form then leaves space to list additional reasons for the appeal. In interviews, appraisers said people could use this portion to detail differences between their valuations and those of similar properties.
You might note, for example, that your roof is 20 years old and needs to be replaced, or that your neighbor has a garage while you don't, or that your house was assessed at significantly more per square foot than similar properties, said Louise M. Jeffers, an appraiser with Reape, Jeffers & Associates.
She noted that it is difficult to get assessments right in mass appraisals such as the review of 579,000 properties that Philadelphia just completed.
If you have an appraisal that is less than about six months old, you may want to submit that with your review form, said Mike Mignogna, president of the Philadelphia Metropolitan Chapter of the Appraisal Institute. Pictures of costly problems can help, too, so go ahead and attach a photo of your leaky roof.
Several appraisers said that it could be worth it to have an appraisal done to boost chances of winning an appeal. Prices for appraisals vary with the type and size of a property but start at about $350.
"An appraiser is going to take a lot of interior pictures of the property and should take good photos of the outside and front and back. Once somebody reads the appraisal, they should feel like they have just visited that property," Jeffers said.
The city's first-level review form also will ask how much you think your property is worth. That section suggests listing separate valuations for the land and for any improvements or buildings, but if you are unable to estimate that, you may list only a total value, said Mark McDonald, a spokesman for Mayor Nutter.
After receiving your paperwork, a city employee may call you to discuss the appeal or ask to see your property. The city could agree with you and lower your assessment, but it also could deny the appeal, or worse - it could decide your property assessment should be even higher.
Property owners who do not agree with the city's decision in the first-level review can still appeal to the Board of Revision of Taxes, or BRT. Appeals to the BRT are due Oct. 7.
Appraiser Frank P. DiFlumeri said many aspects of the new tax system remain unknown, including the percentage rate, or millage, the city will use to calculate a final tax bill. Preliminary forecasts have estimated the tax rate to be at least 1.25 percent of a property's assessment.
City Council will decide that later this year.
Remember, even if you believe your new assessment is outrageously high, you have time.
"The first thing people should do is not panic," DiFlumeri said.
Contact Miriam Hill at email@example.com
or at 215-854-5520. Follow her on Twitter @miriamhill.