When make an appraisal for a home mortgage the bias is for a higher appraised value. When engaging in a property tax appeal the bias is for finding a lower home value.

That, however, does not address the mass appraisal process that communities engage in. Mass appraisals are done cheaply. Often it is the lowest cost service that will hire college students to take the measurements and make observations. Past data is frequently rolled forward. The most expensive property on the block may be used as the point of reference. In equalities are abundant.

Consumer Reports (Nov.1992 v57 nil p.723) published that property tax records show an error rate of 40% exists in estimating property taxes.

The National Taxpayers Union ("How To Fight Property Taxes" 2004 p.1) writes that as many as 60% of all homeowners are over-assessed and not in line with their home value.

If your mortgage payment reflect a surge, it may be because your property taxes have increased. An excellent and inexpensive eBook that can guide you with the calculations you’ll need in the process can be found at http://www.housetaxax.com