California Code, Revenue and Taxation Code - RTC § 20821

(a) A participating county shall charge claimants interest on the amount of property taxes deferred pursuant to this part.  The effective annual interest rate shall be 7 percent, or the effective annual yield earned in the prior fiscal year by the Pooled Money Investment Account plus 2 percent, whichever is higher, rounded to the nearest full percent.

(b) The interest rate provided for by subdivision (a) shall be applied as of the first day of the month in which a deferment payment is made pursuant to this chapter and every day of the month thereafter until the lien is discharged.  In the event that any payment is applied, in any month, to reduce the amount owed under the lien, the interest rate shall be applied to the balance of the amount owed beginning on the first day of the following month.

(c) In computing interest in accordance with this section, fractions of a cent shall be disregarded.