A computer system and method is disclosed that aids assessors in valuing commercial real estate. To support their cost-based value, assessors use the system to generate an income-based value. The user inputs ranking criteria. The system has a database of rents, vacancy rates, expenses, and cap rates that are derived from the market and are specific for application to properties within the assessor's district. The system calculates an income value based on recommended or custom indicators. The system also aids assessors in accurately calculating obsolescence. After the user inputs requested data, the system brings up the trended income value, calculates a percent difference between the cost and income values, and offers an obsolescence analyzer test to determine if there is obsolescence. If there is obsolescence, the system instructs the user on the correct way to apply it, and if not, additional questions are offered to help identify the discrepancy.