Why are my neighbor's and my tax bills different when the houses are the same?

Proposition 13, passed by the voters in June 1978, established 1975 as the original base year value and requires that the base value of a property be established as of the date of change of ownership, or as of the date of completion of new construction. If you and your neighbor purchased your properties in different years or have different construction dates, your base values reflect different market values.