A system and method for determining comparative values of comparable properties based on assessment percentages and sales data of the comparable properties to ultimately determine a value for a subject property. In a first embodiment, the "assessment percentage" is the "base property tax" for the subject property and comparable property. A price/tax factor is computed for each comparable property by dividing the sale (or sold) price of the comparable property by its base tax. The price/tax factor for each comparable property is then multiplied by the base tax of the subject property to generate a net comparative value for each comparable property. To take into account appreciation for recently sold comparable properties, an average appreciation is obtained for the area in which the subject and comparable properties are located. The average appreciation is pro rated to determine the comparative value for each comparable property. On the basis of the comparative values and other pertinent information, the value of the subject property may be set by a real estate agent, bank, appraiser, etc. In second and third embodiments, the "assessment percentage" is the "assessed value" and "phase value", respectively, which are used to compute the comparative values in a manner similar to the first embodiment.