How is a Washington 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. Washington HB 1217 (2024) requires 90 days advance notice for any rent increase, prohibits any increase during the first 12 months, and caps annual increases at the lower of CPI + 7% or 10% flat. Buildings under 12 years old are exempt. The rent cap framework sunsets July 1, 2040. Use a calculator rather than rely on memory; small CPI errors compound over multi-year tenancies.

Source: RCW 59.18.140 (90-day advance notice for any rent increase, HB 1217)