Tacoma's updated Rental Housing Code requires that prospective tenants earn at least 3 times the monthly rent when the monthly rent amount is below the Fair Market Rent (FMR) amount set by the U.S. Department of Housing and Urban Development (HUD) and at least 2.5 times the monthly rent when the monthly rent amount is at or above the HUD FMR.
LandlordSolutions has put together a short guide on how calculate Fair Market Rents for your properties. HUD provides comprehensive FMR databases that housing providers should reference when calculating FMR for your property.
HUD FMR for other populous counties in WA State: