Under the Pennsylvania Constitution, all real estate, whether residential, industrial or commercial, must be taxed on the same basis. In Philadelphia, a single tax is imposed on real estate for the benefit of both the City and the School District. City assessors or evaluators determine the market value for each property on a uniform basis, then calculate the corresponding assessment; and the Department of Revenue then bills property owners for the tax based upon the millage rate determined by City Council and the Mayor. The tax is imposed on a calendar year basis, unlike in many other counties where the school district tax is imposed on a fiscal year basis. The taxing system and its governing legal principles are very complex, although Philadelphia has announced plans for a new simplified process. Real estate taxes should be fair, equitable and uniform, but many inequities can exist in a city with over 565,000 properties. Any property owners who believe their assessments are unfair should seek legal advice about a tax assessment appeal.