You lose your Proposition 13 protection when the county assessor has grounds to reset your property’s assessed value to current market value, and California recognizes two main grounds: a change in ownership and new construction. Both are defined broadly enough to catch transactions people don’t think of as sales or building projects, and a handful of narrower rules, including the parent-child transfer rules rewritten by Proposition 19, decide whether specific transfers count. Knowing how you lose the Prop 13 exemption comes down to knowing which events the assessor treats as reassessment triggers and which ones the law carves out.
What Prop 13 Locks In
When you buy California property, the assessor sets a base year value equal to your purchase price. Each year after that, the assessed value can rise by no more than 2%, no matter what happens to the market, and your tax rate is capped at roughly 1% of that assessed value plus voter-approved local bonds. Over decades the gap between the assessed value and the property’s real market value can become enormous. A home bought for $300,000 in 2000 might carry an assessed value near $480,000 in 2026 while comparable homes sell for $1.2 million. A reassessment event wipes out that gap and starts the clock over at current market value.1California State Board of Equalization. Publication 800-10 Information Sheet
Change in Ownership Is the Main Way People Lose It
Most Prop 13 losses come from a change in ownership. California defines this as any transfer of a present interest in real property, including the right to use it, where the value transferred is substantially equal to the full ownership interest.2California Legislative Information. California Revenue and Taxation Code RTC 60 Selling is the obvious case. So are gifts, most inheritances, adding or removing someone from title, and certain long-term lease arrangements. Reassessment takes effect as of the transfer date, and the county follows up with a supplemental tax bill.
Transfers the Law Excludes Automatically
Not every title change resets your assessed value. Several categories are excluded automatically, without any special claim form:3California State Board of Equalization. Change in Ownership Frequently Asked Questions
- Transfers between spouses or registered domestic partners, including adding a spouse to the deed, transfers through divorce, and transfers on death.
- Moving property into or out of a revocable trust, as long as the person who created the trust keeps the power to revoke it or remains the beneficiary.
- Restructuring how co-owners hold title without changing anyone’s ownership percentage, such as converting a tenancy in common to a partnership where each partner’s share stays the same.
- Adding someone to title as a joint tenant, provided the original owner remains a joint tenant. When that original owner later dies, the survivor’s acquisition of full ownership does trigger reassessment.
- Mortgages, refinances, and other security interests that don’t actually transfer ownership.
Parent-child and grandparent-grandchild transfers work differently. They require a specific claim and follow the stricter rules Proposition 19 imposed.4California Legislative Information. California Revenue and Taxation Code RTC 62
Parent-Child Transfers Under Proposition 19
This is where families most often lose Prop 13 by accident. Before February 2021, Propositions 58 and 193 let parents transfer any property to their children without reassessment, including rentals and vacation homes, with generous value limits. Proposition 19 repealed those rules and replaced them with much narrower ones.5California State Board of Equalization. Exclusions from Reappraisal Frequently Asked Questions
Under Proposition 19, a parent-child transfer avoids full reassessment only if every one of these conditions is met:
- The property was the parent’s primary residence, and the child moves in and uses it as their own primary residence within one year of the transfer.
- The child files for the homeowners’ exemption or disabled veterans’ exemption within one year of the transfer. Miss that deadline and the exclusion only starts the year you finally file, not retroactively.
- The market value at transfer doesn’t exceed the parent’s assessed value by more than $1,044,586 (the adjusted limit for transfers between February 16, 2025 and February 15, 2027). Any excess above the limit gets added to the assessed value.
- The child submits form BOE-19-P to the county assessor within three years of the transfer date and before transferring the property to anyone else.
Grandparent-grandchild transfers follow the same rules, but only when all of the grandchild’s parents who are children of the grandparent are deceased.6California State Board of Equalization. Proposition 19 Fact Sheet
The practical fallout is significant. Investment properties, vacation homes, and rentals passed from parent to child now get fully reassessed with no exclusion available. If a child inherits the family home but doesn’t move in within a year, the exclusion is gone. Estate plans built around the old Prop 58 rules should be reviewed.7California Legislative Information. California Revenue and Taxation Code RTC 63.2
New Construction and Major Remodels
You can lose Prop 13 protection without ever transferring the property. Any new construction triggers reassessment of the added or altered portion. California defines new construction as any addition to real property and any alteration that amounts to a major rehabilitation or converts the property to a different use.8California Legislative Information. California Code RTC 70
The dividing line is between work that creates new value and work that preserves existing value. Adding a bedroom, building a pool, converting a garage to living space, or gutting and rebuilding a kitchen all count as new construction. The assessor assigns a new base year value to the improvement itself and adds that on top of your existing base year value for the rest of the property. Your original Prop 13 base on the unchanged portions stays intact.
Routine maintenance and cosmetic repairs don’t trigger reassessment. Replacing a worn-out roof with a comparable one, repainting, fixing plumbing, and replacing carpet usually count as maintenance. Large-scale renovations blur the line. Modernize a property so thoroughly that it’s essentially the equivalent of a new building, and assessors treat the whole project as new construction even without added square footage.
County assessors watch building permits closely. Pull a permit for a $200,000 kitchen remodel and the assessor’s office will look at it. Skipping permits to avoid reassessment creates worse problems with code enforcement and insurance, and assessors can still find unpermitted work through aerial imagery and property inspections.
LLCs, Corporations, and the 50% Rule
Putting property into a corporation, LLC, or partnership can trigger reassessment if the transfer isn’t structured carefully. As a general rule, transferring real property to a legal entity is a change in ownership. There’s an important exception when the transfer only changes the method of holding title and no one’s proportional ownership shifts.9California State Board of Equalization. Rule 462.180 Change in Ownership – Legal Entities
The bigger trap is indirect. Say you moved property into an LLC years ago without reassessment because everyone’s proportional interest stayed the same. If the original owners later sell or transfer more than 50% of their total ownership in that LLC, the property gets reassessed. Assessors look through the entity to the underlying real estate, which stops people from selling property by selling the entity that holds it. The same 50% threshold applies to corporate stock. When any person or entity acquires more than 50% of the voting stock of a corporation that owns California real property, all of that real property is treated as having changed ownership. Layered entity structures don’t work around the rule; the analysis traces ownership through chains of entities.
Does Renting the Property Out Cost You Prop 13?
Converting your home to a rental doesn’t, on its own, trigger a Prop 13 reassessment. Your base year value and the 2% annual cap stay in place regardless of how you use the property, because Prop 13 protects all real property in California, not just owner-occupied homes.1California State Board of Equalization. Publication 800-10 Information Sheet
What you do lose is the homeowners’ exemption, a separate $7,000 reduction in assessed value available only for owner-occupied primary residences. At a 1% tax rate that’s about $70 a year, so the direct hit is modest.10California State Board of Equalization. Homeowners’ Exemption
The bigger cost is downstream. If your children later inherit the property, the Prop 19 parent-child exclusion applies only if it was your primary residence, so renting it out before the transfer wipes out that option. Renting for long enough also affects federal capital gains treatment when you sell, because the $250,000 exclusion ($500,000 for joint filers) requires the home to have been your primary residence for at least two of the five years before the sale.11Internal Revenue Service. Sale of Your Home
What the Tax Bill Looks Like After Reassessment
Once a reassessment event happens, the assessor determines the property’s current market value and compares it to the prior assessed value. The difference becomes a supplemental assessment, and you receive a supplemental tax bill covering the period from the first of the month following the event through June 30.12California State Board of Equalization. Supplemental Assessment
If the event falls between January and May, you’ll actually get two supplemental bills: one for the remainder of the current fiscal year and another for the entire next fiscal year. These arrive on top of your regular annual property tax bill, and each must be paid by its own due date. Two common mistakes: assuming the supplemental bill replaces the annual bill, and assuming your mortgage escrow will handle it. Many lenders don’t pay supplemental bills from escrow, leaving that on you. The supplemental bill also can’t be offset against your regular bill, even when the reassessment somehow reduced value. Miss the deadline and penalties apply.
Penalties for Not Reporting a Change
California requires buyers and transferees to file a change in ownership statement with the county assessor. If you don’t file within 90 days of the assessor’s written request, a penalty gets added to your tax bill: the greater of $100 or 10% of the taxes on the new base year value, capped at $5,000 if the property qualifies for the homeowners’ exemption or $20,000 if it doesn’t.13California Legislative Information. California Revenue and Taxation Code RTC 482
Legal entity ownership changes are tighter. The entity has to file within 90 days of either the change in control or a written request from the Board of Equalization, whichever comes first. The penalty is 10% of the taxes on the new base year value, without the homeowner-friendly cap.
Fraud is much worse. If a taxpayer’s fraudulent act or omission causes property to escape assessment or be underassessed, the assessor adds a penalty equal to 75% of the additional assessed value, on top of the back taxes.14California Legislative Information. California Revenue and Taxation Code RTC 503
Contesting a Reassessment You Think Is Wrong
If the assessor set your new value too high, you can file an appeal with your county’s assessment appeals board. The regular filing window runs from July 2 through either September 15 or December 1, depending on whether your county mails assessment notices by August 1; most counties use the December date. For supplemental assessments, you generally have 60 days from the date of the supplemental notice.
The most persuasive evidence is comparable sales data: recent sales of similar properties in your area that closed below the assessor’s value. An independent appraisal can strengthen the case, though fees for a single-family home typically run several hundred dollars.