How is a California rent increase calculated when there is a percentage cap?

Take the current monthly rent, multiply by the cap percentage, and that is the maximum dollar increase. For example, a 5 percent cap on $2,000 monthly rent gives a maximum increase of $100, for a new rent of $2,100. Where the cap is "5 percent plus CPI capped at 10 percent" (such as California's AB 1482), look up the relevant regional CPI for the prior 12 months on the Bureau of Labor Statistics website. If CPI is 3 percent: 5 plus 3 equals 8 percent allowed (under the 10 percent cap). If CPI is 6 percent: 5 plus 6 equals 11 percent which is capped at 10 percent. If CPI is negative: only the base 5 percent applies. Round to the nearest dollar. California requires 30 days notice for rent increases of 10% or less and 90 days notice for increases above 10%. AB 1482 caps annual increases at the lower of 5% + local CPI or 10% flat, with exemptions for natural-person single-family owners and buildings under 15 years old. Use a calculator rather than rely on memory; small CPI errors compound over multi-year tenancies.

Source: Cal. Civ. Code 827(b)