Most rent increase mistakes in California are not arithmetic mistakes. The landlord multiplies correctly. They just multiply the wrong rent by the wrong percentage, or use a CPI figure that had already expired on the date the new rent took effect.
Here is the order to work in. Five steps, and the first one decides whether the other four even apply.
Step 1: decide which cap governs the unit
California has two layers. A city rent control ordinance comes first where one exists and covers the unit. The statewide cap, AB 1482, applies to most of what is left.
The statute says so directly. It does not apply to housing already under a local rent control ordinance that limits annual increases to less than the state formula (Cal. Civ. Code § 1947.12(d)(3)). An older apartment in Los Angeles, San Francisco, Oakland, or San Jose usually falls under the city’s number, not the state’s.
So before you open a calculator, answer two questions:
- Is the property inside a city with its own ordinance, and does that ordinance reach this building? The California rent control city list is the place to start.
- If not, is the unit exempt from AB 1482? Newer buildings, some single-family homes and condos, and some owner-occupied duplexes are. The rules are in is my property exempt from AB 1482.
If a city ordinance governs, use the city’s published figure and stop here. If neither applies, neither layer caps the increase, though some cities attach other rules to a large one. If AB 1482 applies, keep going.
Step 2: find the right base rent
The cap is a percentage of the lowest gross rental rate charged for the unit at any time in the 12 months before the increase takes effect. Not the current rent. The lowest one.
Discounts, concessions, and credits the tenant accepted are left out of that figure, and the lease has to list the gross rent and any concession separately (§ 1947.12(a)(1)). A tenant paying $1,850 because of a $50 monthly concession on a $1,900 lease has a gross rent of $1,900.
This is where a second increase inside one year goes wrong. The base does not reset when you raise the rent. It stays at the lowest point of the trailing twelve months.
Step 3: pull the CPI figure for your county and your date
The statute names the index by county (§ 1947.12(g)(1)):
| Counties | Index |
|---|---|
| Los Angeles, Orange | CPI-U, Los Angeles-Long Beach-Anaheim |
| Riverside, San Bernardino | CPI-U, Riverside-San Bernardino-Ontario |
| San Diego | CPI-U, San Diego-Carlsbad |
| Alameda, Contra Costa, Marin, San Francisco, San Mateo | CPI-U, San Francisco-Oakland-Hayward |
| Everywhere else | California CPI from the Department of Industrial Relations, where BLS publishes no index for the area |
Then match the figure to the effective date of the increase, not the date you write the notice. An increase that takes effect on or after August 1 uses the change from April of the prior year to April of this year. One that takes effect before August 1 uses the year before that. Where there is no April figure, March is used instead, and the result is rounded to the nearest tenth of a percent (§ 1947.12(g)(3)).
Step 4: apply the formula
Add 5 percent to the CPI change. If the total is over 10 percent, the cap is 10 percent.
For increases taking effect from August 1, 2026 through July 31, 2027, two regions have published figures from county agencies:
- Los Angeles metro: 3.7 percent CPI, cap 8.7 percent (LA County Department of Consumer and Business Affairs).
- San Francisco-Oakland-Hayward: 3.8 percent CPI, cap 8.8 percent (County of Marin). An increase in that region that took effect before August 1, 2026 was capped at 6.3 percent.
For Riverside, San Diego, or a county on the fallback index, look up the figure for your date before you rely on any number. The AB 1482 rent increase limits page has more on the regions. The AB 1482 calculator turns the formula into a dollar amount; check that the CPI it shows matches your region and your effective date before you rely on the result.
A worked example, with the common mistake
A San Mateo County unit leased at $2,300 a month. On March 1, 2026 the rent went to $2,400. The landlord now wants a second increase effective November 1, 2026.
The tempting math is $2,400 times 1.088, which is $2,611.20. That is wrong.
The lowest gross rent in the 12 months before November 1 is $2,300. The cap for a November 2026 effective date is 8.8 percent. So the ceiling on the rent is $2,300 times 1.088, or $2,502.40. The landlord can add $102.40, not $211.20.
Two more limits apply in the same example. A tenant who stays in the unit can be increased in no more than two increments over any 12-month period (§ 1947.12(a)(2)), and the March increase was the first. And a new tenancy, where no prior tenant remains, can start at any rent. The cap applies to increases after that starting rent is set (§ 1947.12(b)).
Step 5: check the notice period
An increase of 10 percent or less, counting every increase in the prior 12 months, needs at least 30 days’ written notice. Above 10 percent, it needs 90 days (Cal. Civ. Code § 827(b)). Notices sent by mail get extra days on top of that. The details are in rent increase notice periods in California.
What an overcharge costs
A tenant who paid more than the cap can sue for the overage, plus attorney’s fees at the court’s discretion. If the court finds the landlord acted willfully, damages can reach three times the overage. The tenant has three years to bring the claim, and the Attorney General and the local city attorney can enforce it too (§ 1947.12(k)).
Three years of a $100 overage is $3,600. Tripled, it is $10,800. Worth an extra ten minutes on the base rent.
This is general information, not legal advice. Rules change and local ordinances vary. Confirm current requirements with your city, county, or an attorney before you act.
Once the number is right
Write the new rent and the effective date into the notice, deliver it the way the statute allows, and change the rent on the lease record so the next invoice actually bills it. Rent payments in LeaseRooster pick up the new amount from the effective date, autopay included.