Calculate the maximum rent under a percentage cap, a CPI-plus rule or California AB 1482, and check a proposed rent and its percentage increase.
Rent Increase Cap Formula
A percentage cap limits a covered increase over a specified period and base. A common CPI-plus model adds a fixed number of percentage points to inflation and applies a hard ceiling. This calculator’s custom model also floors a negative combined rate at zero; verify that this convention matches the actual rule:
Custom modeled percentage = max(0, min(CPI + Fixed, Hard Cap))
After verifying the applicable percentage and calculation base, the arithmetic ceiling follows below. In flat and custom modes, Base Rent is the entered current gross monthly rent. In AB 1482 mode, Base Rent is the lowest gross monthly rent charged during the 12 months before the proposed increase; an intervening increase does not reset that base:
Modeled Maximum = Base Rent * (1 + Percentage / 100) Remaining Room = max(0, whole-cent maximum - Current Gross Rent)
Variables:
- Current Gross Rent is the current gross monthly rate, entered in whole cents
- CPI is the applicable percentage change, not an index-level number. AB 1482 requires the statutory index and effective-date comparison, rounded to the nearest 0.1%
- Fixed is the addition in percentage points; the covered AB 1482 formula uses 5 percentage points
- Hard Cap is the percentage ceiling. AB 1482 uses the lower of 5% plus the statutory CPI or 10%; zero in custom mode means no increase
Some rules use a flat percentage. The optional proposed-rent check compares whole cents against the modeled ceiling without a half-cent tolerance. The displayed maximum is rounded down to a whole cent, a conservative arithmetic convention rather than a determination of legally required rounding. At or below that amount does not establish that an increase is lawful.
Examples of Rent Cap Rules
Rent-cap rules differ widely, and many units are exempt. These examples show the range of approaches; always confirm the rule that applies to your unit.
| Approach | How the cap works |
|---|---|
| California (statewide) | Covered AB 1482 tenancy: lower of 5% + statutory CPI or 10%, using the lowest prior-12-month gross rent |
| Flat percentage cap | A single fixed limit, such as 5% or 7%, per year |
| CPI-only cap | Tied to inflation alone, sometimes with a floor and ceiling |
| No cap | No general percentage cap; lease, notice and other protections may still restrict increases |
Coverage and exemptions have specific conditions. For example, California’s separate-title property exemption has ownership and notice conditions; simply being a single-family home is insufficient. Local rent controls and other protections may be stricter. Verify current guidance from the California Attorney General and the governing law. Notice and permitted timing are separate from the arithmetic cap.
Example Problems
Example 1: A flat percentage cap.
Assume a verified 5% rule applies to a $1,800 gross monthly base with no earlier increase affecting the calculation. The model gives 1,800 × 0.05 = $90 and a ceiling of $1,890. A proposed $1,950 is $60 above that modeled monthly ceiling. Coverage, notice and the lease still require separate verification.
Example 2: The California 5% + CPI rule.
Assume a covered AB 1482 tenancy has a lowest prior-12-month gross rent of $2,000 and an applicable statutory CPI of 3%. The modeled cap is min(5% + 3%, 10%) = 8%, giving a $2,160 ceiling. If current gross rent is already $2,100 after an earlier increase, remaining arithmetic room is $60, not another 8% of $2,100. The statute also limits increments during a 12-month period; this calculator does not check increase dates or counts.
Frequently Asked Questions
How much can my landlord raise the rent?
It depends on location, property coverage, prior increases, the lease and other protections. Absence of a general percentage cap does not remove notice, lease, anti-retaliation, anti-discrimination or applicable emergency restrictions. This calculator checks only the selected arithmetic model.
What is the most rent can go up in California?
For a covered tenancy under Civil Code §1947.12, the percentage limit is the lower of 5% plus the statutory CPI change or 10%, measured from the lowest gross rent in the preceding 12 months. Qualifying separately stated concessions are excluded when determining gross rent. CPI depends on geography and the proposed effective date: before August 1 use the preceding April-to-April comparison, and on or after August 1 use the current April-to-April comparison, with the statutory March fallback where needed; round to 0.1%. Confirm the published applicable figure. Local rules, exemptions, the number of increases, lease and notice requirements also matter.
Does a rent cap apply to every apartment?
No. Exemptions differ by jurisdiction and have specific conditions. California examples include certain newer buildings, qualifying owner-occupied duplexes and separately titled properties meeting statutory ownership and notice conditions. Other covered housing can have stricter local rules. Verify the unit’s status and current requirements; the calculator does not decide eligibility or exemptions.
