If a tenant has a lease for more than 30 days, the rent cannot be increased during that lease unless the lease provides for an increase.
By comparison, if the tenant has a periodic rental agreement (e.g., month-to-month), the landlord can increase the rent but the landlord must give proper advance notice in writing. This writing must also inform the tenant how much the rent will increase and when the increase goes into effect. The notice can be delivered two ways: one, by personal delivery, or two, by first class mail.
Under California law, the landlord must give at least 30 days advance notice if the rent increase is more than 10 percent (or less) of the rent charged at any time during the 12 months previous to when the increase takes effect. A 60 day notice is required where the rent increase is greater than 10 percent. If the landlord chooses to serve the notice by mail, the landlord must give the tenant an additional 5 additional days advance notice, i.e., 35 or 65 total days prior to the schedule increase.