Since its passage, Proposition 13 prohibits property tax increases until property ownership is changed.

If either spouse is over age 55 (when the old home is sold), PROP 60 allows replacement of a primary residence with a new home of equal or lesser value (but see below) within the same county and transfer of the Prop 13 assessed valuation from the old home to the new property.  This is allowed once in your lifetime, and a spouse who has done it before 'taints' both spouses.

PROP 90 allows counties to elect to accept transfers of Prop 13 values for moves from other counties when a primary residence is replaced with a less expensive (but see below) home. If you are over 55 and move into a county which accepts Prop 90, you may take your old, lower Prop 13 value, regardless of from which county you move.

Using Prop 90, you can sell your $400,000 San Francisco home [assessed value $80,000] and move to a new $300,000 home in San Mateo; the new San Mateo assessed value will be $80,000!

Alameda,  Los Angeles, Orange, San Diego, San Mateo, Santa Clara, and Ventura. [Contra Costa, Inyo, Kern, Riverside, Modoc, Monterey, and Marin have dropped out of the Prop 90 program.]

Props 60 and 90 apply if you "trade down" (i.e. the new home costs less than the sales price of the old home). 

  >  If you buy New Home 1^st; then sell the Old Home, you must go down in price.

•         In 1^st 365 days after the sale of Old Home, you may go up 5% in the purchase price of New Home.
•         If you buy New Home more than 1 year from the sale of Old Home, but less than 2 years, you may go up 10%.