Can a California landlord increase rent retroactively?
No. A rent increase in California only takes effect on or after the effective date stated in the notice, and only if the advance notice period was met (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.). A landlord cannot demand back-dated rent at a higher rate for past months. Doing so makes the increase void as to the back-dated period. The tenant continues to owe the original rent for any month already in progress when the notice was served.
Source: Cal. Civ. Code 827(b)
This is an informational answer based on Cal. Civ. Code 827(b) as of early 2026. It is not legal advice. Housing law changes year to year and local ordinances (especially in rent-controlled or rent-stabilized cities) can override or add to state law. For contested cases, consult a California-licensed attorney.