Cities with rent control usually allow rent increases at the Consumer Price Index (CPI measures changes in the price level of a market basket of consumer goods and services purchased by households… and is a statistical estimate constructed using the prices of a sample of representative items whose prices are collected periodically.” see Wikipedia). Landlords can usually bank increases (add together the years that they did not raise the rent with the current year). It is extremely important that you contact your local rent board if you live in a jurisdiction with rent control and your landlord raises your rent by an amount that seems improper. San Francisco and Berkeley have rent board counselors who you can consult with to make certain that your rights are not being violated. It is likely that other rent controlled jurisdictions have counselors or at least employees who can give some informal advice on rent increases and other matters.
State law requires that landlords give a 60 day notice for all rent increases which are more than 10% of the base rent (this is all within any 12 month period and it is cumulative) and a 30 day notice for less than 10% (See Calif. Civil Code Section 827). Rent increases cannot be for retaliatory or discriminatory reasons under both state and local laws.
In rent controlled jurisdictions, once a unit is fully vacated the rent can be raised to market rent (whatever the market will bear). The laws around subletting and vacancies by original tenants or tenants to whom rent control for a particular unit is attributed are highly complex and tenants should consult an attorney or the local rent board to learn your rights. Tenants who do not have rent control at the local level are covered by the laws of the State of California.
Ascertaining if a rent increase is proper on one’s own can be a mistake as the law on rent increases can be very challenging to understand if one is not intimately familiar with the laws, rules and regulations applicable to residential rent increases.